The Audomarois marsh: history, fauna, flora and traditions
The Saint Omer marsh, a natural area recognized by UNESCO
The marshes of Saint-Omer and Clairmarais: a must-see destination in Audomarois
Just 40 minutes from Calais and Dunkirk, and 1 hour from Lille, the Audomarois marsh opens the doors to a world apart. This natural gem of the Hauts-de-France region awaits you for an exotic getaway, rich in history and authenticity.
On the agenda: guided boat tours, rowing and motorboat rides, hiking and biking, and cultural outings in the beautiful town of Saint-Omer. A real breath of fresh air between city and nature!
Located between inland Flanders to the east and the hills of Artois to the west, the Audomarois marsh extends across 15 communes in the Nord and Pas-de-Calais regions. These include: Saint-Omer, Clairmarais, Serques, Éperlecques, Houlle, Moulle, Salperwick, Tilques, Saint-Martin-lez-Tatinghem, Longuenesse, Arques, Watten, Saint-Momelin, Noordpeene, and Nieurlet.
The Audomarois marsh in a few words
This labyrinth of land and water stretches over 3 hectares (700 km²), crisscrossed by more than 37 kilometers of waterways, 700 of which are navigable! These figures attest to the immensity of this natural gem, classified as a Biosphere Reserve by UNESCO. But beyond its dimensions, the Audomarois marsh also impresses with its historical richness and its major ecological role.
In the past, this vast peaty wetland was still influenced by the high tides via the Aa River, particularly during the Carolingian era. Gradually, humans took over these lands: the monks of Sithiu (the former name of Saint-Omer) and the Clairmarais Abbey extracted peat from them. Farmers poldered the land, dug drainage canals to channel water to the sea, and channeled the main waterways to enable the growth of trade in Saint-Omer.
In the 19th century, the marshland took on its current form: a space that is simultaneously inhabited, wild, and cultivated. Market gardeners still perpetuate the tradition of growing Saint-Omer summer cauliflower and winter endive.
A discreet destination but full of surprises, the last market garden marsh in France delights hikers, fishermen and nature lovers in search of peace and authenticity.
Climb aboard traditional boats—escutes and bacôves—for a trip along the water. The region's last remaining boat builders invite you to experience a unique cruise in the heart of a landscape shaped by man and preserved by nature.
Let’s discover the Audomarois marsh together: its history, its fauna, its flora… and its well-kept secrets.
In summary
The Audomarois marsh in a few figures
As mentioned above, the Audomarois marsh covers 3,726 hectares, or just over 37 km². It is the largest wetland in the entire Hauts-de-France region.
To give you an idea of its size, the marsh is about 12 times larger than the Amiens market gardens, and it has four times as many rivers . This vast natural basin has an average elevation of 0 meters, and some areas can drop to as low as one meter below sea level . This configuration makes the area highly vulnerable to rising water levels.
Although a few hundred hectares belong to public actors (the Hauts-de-France Region, the Pas-de-Calais Department, Eden 62, the municipalities of Saint-Omer and Clairmarais, the Regional Natural Park, the Coastal Conservatory…), 90% of the marsh is private.
It has more than 13,000 plots of land distributed among 5,000 owners.
On the agricultural level, the marsh includes approximately:
450 hectares of market gardening (including the famous cauliflower of Saint-Omer);
300 hectares of various crops (including cereals);
1,000 hectares of meadows , part of which is used for cattle and sheep farming.
This mosaic of owners and uses makes the Audomarois marsh a living, agricultural and fragile territory , both shaped by man and subject to natural hazards.
The Audomarois marsh: 13th century of labor
The Saint-Omer marsh during Antiquity
A marsh developed by monks in the early Middle Ages
In the 7th century, during the reign of Dagobert I, three monks from Luxeuil—Mommelin, Bertin, and Ebertram—settled in Morinie. Their mission: to convert the pagan Morin people to Christianity. At their head was Bishop Audomar of Thérouanne, a powerful figure in the clergy of the time.
The first monastery was founded on the present-day site of Saint-Mommelin. But the location, too exposed to flooding and attacks, quickly proved unsuitable.
According to legend, the three monks then boarded a boat and let themselves be carried by the waters, praying to God to guide them. They eventually landed on the heights of Sithiu , a more favorable, sheltered and elevated place.
Another version of the legend tells that these lands belonged to a pirate named Aldroad . Converted by Audomar, he supposedly offered all his lands to the clergy, encompassing the territories of the future communes of Saint-Omer, Clairmarais and Arques.
From Sithiu to Saint-Omer, a stronghold in the North
Unlike Saint-Mommelin, located on the edge of the marsh and close to the Gulf of Portus Itius, Sithiu offered many advantages:
A natural elevation of 12 meters, ideal for spotting enemies
A marsh surrounding the area on three-quarters of its length, forming an effective natural barrier
This strategic choice proved to be wise, as Saint-Omer would suffer several waves of Viking invasions in the 9th century (→ see our dedicated article).
Gradually, the site developed: construction of the lower abbey (Saint-Bertin, initially dedicated to Saint-Pierre), the upper church (future cathedral), then a fishing village.
From the 10th century onwards , Saint-Omer became a dynamic market town at the crossroads of Flanders and Artois.
In the 12th and 13th centuries, it became an important trading port, a religious and administrative stronghold, and an intellectual center of the Counter-Reformation during the Renaissance.
Saint-Omer developed from the XNUMXth century
In the 9th century, monks undertook the first hydraulic engineering projects in the marsh. One of the major projects was the diversion of the Aa River towards Arques , thanks to the creation of the Basse-Meldyck Canal . This canal, whose name means "flour" in Flemish ( maldyck ), supplied water to a local mill.
A second structure, the Haute-Meldyck , was then dug to carry the water to the foot of the Abbey of Saint-Bertin.
Around the 10th century, the first polderization operations began in the Audomarois marsh. The principle: to drain certain parts of the marsh to gain arable land.
The furrows left by the Aa in the marshy basin are then widened and deepened to facilitate water flow . The extracted silt is used to raise the level of agricultural and livestock land.
This technique was applied gradually, in a logical order: from the high marshes (on the outskirts of the towns) towards the low marshes (in the heart of the marsh). This process of land conquest extended until the end of the 17th century.
From there, techniques from the Dutch polders were adopted : reclaiming the low marsh, dikes, water gates, and wind-powered drainage mills to manage the levels.
In 1866 , the conquest of land came to an end: no more new land would be “reclaimed from the water”.
Canal works and the era of maritime trade
In addition to creating agricultural land and drainage ditches called watergangs , the inhabitants also had to fight against flooding and develop navigation.
Around the year 1100 , a vast canal named Nova A — or “Grand Large” — was dug. It crossed the marshes of Salperwick, Tilques, Serques, Houlle and Moulle.
This new river route allows larger boats to circulate and facilitates the flow of water from the Aa to the sea , thus reducing the risk of flooding.
In 1165 , the Grande Rivière was in turn transformed into a canal. It served the inland ports of Saint-Omer —notably the Quai du Haut-Pont, the Quai Vain, and the Quai des Salines—and connected them to the maritime port of Gravelines . This project was initiated by Count Philip of Alsace.
These hydraulic structures have a dual purpose: drainage and economic development.
Meanwhile, Count Baldwin VII of Flanders continued the work begun by his predecessor, Baldwin VI , who had already connected the Lys basin to the Aa basin via a wide defensive ditch. This ditch would later become the famous Neuffossé canal.
Finally, to better control the water downstream, a dike was built on the Flemish coast , making it possible to contain the high tides and to secure the land upstream.
Some key dates in the evolution of the Audomarois marsh
The history of the Audomarois marsh is also marked by a series of major technical developments. Here are some key milestones:
1681 : Creation of the Calais canal , aimed at improving river connections to the sea.
1699 : Construction of the Vauban lock at Gravelines . It allows the regulation of high tides by closing to prevent seawater from flooding the Aa, and opening to facilitate its flow towards the sea.
1753 : Creation of the Neuffossé Canal , linking the Aa and Lys rivers . This project strengthened navigation routes between the North Sea and the inland areas. This canal was equipped with a boat lift (the Fontinettes lift). This lift was capable of lifting barges over a difference in elevation of 13,13 meters!
From there, waterways made it possible, particularly during the Industrial Revolution, to connect Dunkirk to Lille via a series of canals:
Colme canal ,
Aa canal ,
Neuffossé canal ,
Lys Canal ,
then the Deûle.
This river organization fully integrates Saint-Omer into the major river trade routes of the North.
1958 : The last major upheaval in the Audomarois marshland occurred with the closure of the Haut-Pont canal section and the creation of the large-gauge canal . This new route bypassed the town to accommodate barges much larger than the old Freycinet models.
Since then, heavy boats have been excluded from the town and now cross directly into the natural area , profoundly altering the geography and uses of the marsh . In 1967, the Fontinettes boat lift was permanently replaced by a high-fall lock.
A space recognized by UNESCO and other prestigious labels
RAMSAR and PNR
The Audomarois marshland is supplied by a complex hydraulic network:
the Aa River ,
rainwater and runoff ,
as well as two deep aquifers , which play a key role in its ecological balance.
This territory is one of the two major wetlands of national and international importance in the Nord–Pas-de-Calais region , alongside the Scarpe–Escaut area.
As such, it benefits from several official protections :
It is classified as a Ramsar site , according to the international Ramsar Convention signed in 1971 for the preservation of major wetlands in the world.
It also includes a Regional Natural Park (PNR) , that of the Étangs du Romelaëre , recognized for its remarkable biodiversity and its role in hydraulic regulation.
This recognition confirms the importance of the Audomarois marsh as a reservoir of biodiversity, a regulator of floods , and an exceptional natural heritage.
Since 2013 , the Audomarois marsh has also been classified as a Biosphere Reserve by UNESCO , as part of the MAB (Man and Biosphere) program.
This recognition celebrates the unique balance between a remarkable natural ecosystem and a territory shaped by human activity for over a thousand years.
Here, man and nature are interdependent . Without regular interventions — such as dredging canals, cutting weeds or maintaining banks — the marsh would gradually return to its former wild state: an impenetrable wetland that is difficult to inhabit.
This work of management and maintenance , passed down from generation to generation, is what allows the Audomarois marsh to remain today:
reside ,
cultivated ,
and welcoming to exceptional biodiversity.
The Saint-Omer marsh: perpetual maintenance
A maintained, inhabited and shared marsh
The maintenance of the Audomarois marshland is now entrusted to the seventh section of the water management services , a structure dedicated to water management. Depending on the season, its agents intervene to:
dredging the rivers ,
to cut down the algae ,
and to reinforce the banks , in particular through the technique of fascine laying (laying bundles of branches to stabilize the banks).
To carry out these operations, specialized equipment is mobilized: cranes, barges, mowers, etc.
In the past, these tasks were carried out by hand, using traditional tools such as:
the trouspa (for repairing the riverbanks),
the edrack (for digging ditches),
the shovel (for extracting peat),
the baguette (a sturdy dip net for pulling out mud).
Today, the marsh is a living, shared territory . You'll find the following there:
inhabitants ,
market gardeners and livestock farmers ,
fishermen , hunters, walkers and tourists ,
as well as sports enthusiasts , particularly in canoeing or cycling.
They all coexist in respect of a fragile balance , necessary for the preservation of this exceptional natural environment.
The Audomarois marsh in the global network of biosphere reserves
Since 2013, the Audomarois marshland has been one of the 12 French biosphere reserves recognized by UNESCO, alongside emblematic territories such as:
the Camargue ,
the Cévennes ,
the Fontainebleau forest ,
the Gorges du Gardon ,
the archipelago of Guadeloupe ,
or the Fango valley in Corsica.
It is integrated into the global MAB (Man and Biosphere) network , which aims to:
reduce biodiversity loss ,
to improve the livelihoods of local populations ,
to support sustainable development ,
and promote the exchange of expertise on a global scale.
This classification reinforces the Audomarois marsh in its role as a living laboratory , where the balance between nature, culture and human development is at the heart of priorities.
Natural heritage: the fauna and flora of the Audomarois marshes
Thanks to its temperate climate , abundance of water and rich peaty soils , the Audomarois marsh is home to exceptional flora.
It includes:
over 100 remarkable plant species ,
including 25 protected species ,
and more than 60 plant communities , some very rare or threatened.
The marsh alone is home to 50% of the aquatic flora of the Nord-Pas-de-Calais region . A true plant sanctuary , unique of its kind!
On the fauna side, the latest inventories are just as impressive:
240 species of birds nest in or pass through the marsh, including:
the little bittern ,
the bittern ,
the marsh harrier ,
the great crested grebe ,
and the kingfisher.
26 species of fish inhabit its waters: pike, zander, European eels…
And in the watergangs, rivers and ponds, live many amphibians (green and brown frogs), dragonflies and grass snakes.
Some species are now threatened , such as the European common eel , a victim of river fragmentation.
Others, however, proliferate in a problematic way : this is the case of the muskrat , which digs tunnels in the banks and damages the crops of market gardeners.
Cultural heritage of the Audomarois marshes and old memories
Visitors who appreciate historic architecture cannot travel through the Audomarois region without stopping in the old town of Saint-Omer . Its majestic cathedral , ancient alleyways, and rich history make it an unmissable destination.
Around the town, the marsh villages also bear witness to a remarkable heritage . In Clairmarais , one can still admire an old medieval farm , the ruins of the Cistercian abbey , the Romelaëre ponds reserve and the Rihoult-Clairmarais state forest.
Whether on foot, by bike or by boat, the destination captivates with its timeless charm . It is no coincidence that, as early as the 17th century, the bourgeois of Saint-Omer and Clairmarais appreciated the famous "water walks".
Ancient accounts even claim that every good visitor had to contemplate the "floating islands" of the marsh. These were then piles of earth and vegetation forming veritable natural rafts, drifting with the water.
King Louis XIV himself , after taking Saint-Omer in 1677, is said to have lingered there.
These floating islands have now disappeared, gradually swallowed up by their own weight or destroyed by successive hydraulic developments. But their memory still floats in the marsh's atmosphere...
Flemish origins
While walking through the Audomarois marsh, the attentive walker will notice many names of rivers, ditches or places with Dutch-sounding connotations.
Names like Stackelwaert , Hongarwaert , Bogarwaert , Petite Meer , Grande Meer , Westbrouck , Petit Leeck or Grand Leeck punctuate the landscape, particularly in the marshes of Saint-Omer , Clairmarais , Saint-Martin-lez-Tatinghem , Salperwick , Tilques and Serques.
These names are linguistic vestiges of the Flemish origin of the Audomarois and testify to the antiquity of the hydraulic network.
Here are some keys to understanding:
Meer means “lake” → the “Little” and “Great Meer” are former lakes that have been converted into polders;
Leeck means “leak” or “outlet of a polder”;
Waert = canal;
Brouck = marsh;
Strom = current or flow.
These terms reflect an ancient, highly technical relationship between humans and water , originating from Flemish culture.
Other names, this time in French , have appeared more recently. They often refer to canals or areas developed after the annexation of Saint-Omer to France in the 17th century.
This is the case for names like:
La Redoute ,
The Duck Farm ,
La Riverette ,
Le Mussent ,
or areas once known for their floating islands.
This contrasting toponymy tells the story of the territory , between Flemish culture, hydraulic development and French influence.
A specific rural habitat - The traditional marsh house
Once upon a time, the market gardeners of Saint-Omer
The marsh was cultivated as soon as it was first drained. The first so-called highlands appeared on the outskirts of the city from the XNUMXth century before gradually reaching the old muddy marsh crossed by the Aa.
The market gardening boom of the 18th and 19th centuries
The marshland population experienced significant growth in the 18th century . The gradual end of the feudal system allowed for a better distribution of land and encouraged the establishment of numerous market gardening families.
It was at this time, in 1751 , that summer cauliflower was planted for the first time in the fertile soils of the Audomarois marsh. This vegetable would become one of the agricultural emblems of the territory.
Then came the Industrial Revolution , which transformed the local economy. In 1848 , the arrival of the railway opened up new markets for market gardeners. Vegetables from the marsh could now be shipped quickly to large cities , particularly Paris.
In the summer season, in May-June, the four-season merchants roam the streets of the capital, loudly extolling the qualities of the "First Saint-Omer" : fresh vegetables, straight from the marsh.
The market gardeners of the Audomarois marsh during the Belle Epoque
Between 1850 and 1870 , nearly 400 families settled to cultivate the lands of Saint-Omer , Clairmarais and neighboring towns.
This period coincides with the decline of peat extraction , which was long carried out by peat cutters , the former peat harvesters of the Audomarois marsh.
The advent of coal , mined extensively in the coalfields of Artois , rendered this plant-based fuel obsolete. Peat would only be used again during times of war or shortage.
To compensate for this loss of activity, market gardeners are turning to new crops.
In 1920 , they began producing winter endive , a vegetable that provided a supplementary income during the off-season.
Alongside summer cauliflower , endive became another local agricultural specialty , illustrating the adaptability of the marsh inhabitants.
Market gardening after the war
After the Second World War, traditional market gardening in the Audomarois marsh began a slow decline.
International competition , technological advances , and the emergence of new modes of production are making this type of agriculture increasingly difficult to maintain.
In the past, the marshland plots were only accessible by boat . The market gardener used the bacôve , a flat-bottomed boat, propelled by a pole. It served to transport his harvests—sometimes up to 3,5 tons of cauliflower —but also his horse , essential for working the land.
In the post-war period, some went so far as to pair two or three flat-bottomed boats side by side to load a tractor , illustrating attempts to adapt to modernity.
Alongside the bacôve, the escute served as a small utility boat. More maneuverable, it was used to transport the family, tools or small loads.
She slid through narrow rivers and maneuvered with a ruie , a long, flat oar used as a lever or sculling oar.
Before the arrival of internal combustion engines, then electric ones, some well-to-do market gardeners equipped their boats with a motor-oven, the ancestor of the outboard motor.
The great land consolidation (1972 - 1984)
In the late 1970s , the Audomarois marsh was profoundly transformed by a vast land consolidation operation.
Farm roads and bridges are being built, making more than 500 hectares accessible by land.
From then on, the traditional boats become useless, relegated to secondary or tourist uses.
The boat makers, once indispensable, are closing the doors of their workshops one by one.
Mechanization then offered a breath of fresh air to local market gardening, allowing the activity to survive in the face of increasing competition.
But the decline is clear. The number of families making a living from market gardening is decreasing decade after decade:
200 in the 1970s,
110 to the end of the 1990s,
60 to the end of the 2000s,
and less than 35 today.
This slow disappearance marks the end of an ancestral way of life , that of a marsh cultivated by water, for and with water.
Market gardening today - Between traditions and adaptation
Today, the market gardeners of the Audomarois marsh continue their activity with varied approaches.
Some work in monocultures, alternating cauliflower in summer et winter endive. Others perpetuate a diversified agriculture, sometimes in organic cultivation.
In total, nearly 50 varieties of vegetables are still cultivated in the marsh. Among them:
summer cauliflower ,
winter endive ,
cabbage ,
celeriac ,
the Large Green artichoke from Laon ,
and the Tilques carrot , emblematic of the territory.
In the cultivated marshes, it is not uncommon to come across a market gardener or a seasonal worker , up as early as 4 a.m. , working “in the cool of the morning” to harvest the cauliflowers.
The cooperative expects them in the late morning: deliveries are often made before noon , to ensure the freshness of the product.
This scene is repeated every year, especially between July and August , during the “full” period , when the summer cauliflower is at its peak.
A know-how that endures, between ancestral gestures and contemporary realities.
Peat extraction, hemp cultivation and fishing in the Audomarois marsh
In addition to the market gardening activities entrusted to the brouckaillers , the Audomarois marsh has long allowed the development of other economic activities.
Peat was extracted there , notably for use as fuel for domestic heating. Many of the current ponds , such as the Romelaere pond , are remnants of these former extraction areas.
The marsh also supported the cultivation of hemp , intended for the manufacture of boat ropes.
The inhabitants, for their part, were also excellent fishermen , inventive and ingenious.
Fishing techniques of yesteryear
While today only line fishing is allowed (and only with a valid fishing license ), it was very different in the past.
At that time, various methods were practiced, often collective and ingenious , which are now prohibited:
fishing with a net or drum ,
the weasel , a trident planted in the fish
eel traps and bundles ,
the puchette and the poisenette , handcrafted landing nets.
These popular practices, passed down from generation to generation, are part of the living heritage of the marsh , although their use has disappeared.
Tuft fishing, a specialty of Audomarois
Before the European eel became a protected species, the people of Audomarois practiced a typical fishing method: fishing with a tug.
The method involved agitating a ball of earthworms weighted with lead in the water until an eel took the bait. It was then necessary to hook the eel with a sharp jerk , before it could reflexively open its mouth, and then capture it in an inverted umbrella.
This ancestral gesture, now obsolete, testifies to a fine knowledge of animal behaviour , and to an intimate link between man and his marsh.
The traditional festivals of the Audomarois marshes
While some festivals have disappeared over time — such as the Lyzel procession , formerly composed of floats parading between the Clairmarais road and the Saint-Martin street in Saint-Omer — others continue to draw crowds.
Two major events still make the hearts of Audomarois beat faster every summer:
The Haut-Pont nautical procession , organized on the last Sunday of July . In this emblematic suburb, decorated boats parade on the water, to the applause of the crowd.
The boat pilgrimage on August 15th , towards a statue of the Virgin located at the confluence of the Grand Large and the Écou river , in Tilques . This spiritual and popular event combines contemplation and attachment to the marsh.
The city of Saint-Omer also maintains the tradition of carrying giants from the North.
Batistin , the central figure, represents a gardener from the Bachelin marsh.
He is accompanied by his partner Belle-Lyze.
A true popular mascot , Batistin has lent his name to several local projects, testifying to the vitality of this figure in the culture of Saint-Omer:
– A cheese produced by the Milou farm in Tatinghem
– A bacôve of the Maison du Marais
– A gîte de France in St Omer, at the gateway to the Audomarois marsh
– A shared garden in the heart of the city
A walk in the marshes of Saint-Omer and Clairmarais
The best way to discover the Saint-Omer and Clairmarais marshes is undoubtedly by boat.
Aboard a traditional flat-bottomed boat , the last remaining boat builders invite you on a leisurely journey along the waterways , between peaceful rivers, cultivated fields , and wildlife . An authentic and unique experience awaits , in the heart of a landscape shaped by human hands for centuries.
For those who enjoy land-based walks, the marsh also offers several farm tracks , walking trails and hiking circuits accessible on foot or by bicycle.
Among the most popular routes:
the Lansbergue trail , between Tilques and Serques ,
and the basin path , linking Clairmarais , Nieurlet and Noordpeene.
👉 Consult the complete booklet of hiking trails in the Audomarois region here (PDF)
Finally, the Romelaere nature reserve , a stone's throw from Clairmarais, offers a trail of more than 2 km , marked and accessible to people with disabilities.
Birdwatching hides are located along the path, allowing visitors to discover:
pollarded willows ,
wet meadows ,
the former peat bogs , now ponds,
and many species of birds, some of which are protected.
To enhance your visit, a free audio guide is available at the park entrance, at the Grange Nature , a reception and environmental awareness area.
Whether on the water, on foot or by bike , the Audomarois marsh reveals itself with humility and majesty , provided one takes the time to listen to it.
