Park at the Grange Nature car park in Clairmarais.
(S/E) Head towards the marshes and turn right after the small bridge (signposted: Circuit de Booneghem).
Follow the Booneghem river and cross the marshes, which are home to Saint-Omer's emblematic cabbages and cauliflowers, which you can buy from the market gardeners just outside Clairmarais.
(1) Take the metal footbridge, on your right, to cross the river and follow the Chemin des Abbesses, along the river, which bends to the left towards a road.
(2) At the end of Chemin des Abbesses, turn left onto Route de Booneghem. Pass the inn of the same name. At the crossroads with the Chemin du West Brouck, turn left to continue through the village of Booneghem.
(3) At no. 58 Route de Booneghem, turn left onto the narrow path and enter the nature reserve. Continue due south to the 1er chain ferry, the star attraction of this hike.
(4) Cross the Zieux and turn right to the drawbridge.
(5) Cross the Zieux again to visit the Romeläere Nature Reserve. Follow the footbridges. You can continue to the observatory and make a loop, or turn left to the 2° chain ferry (marked).
(6) Cross the Zieux again, using the chain ferry, then turn left to Rue du Romelaere and join the Grange Nature car park (S/E).