An association of nature guides, all of them local, running the full range of Baie de Somme outings: the crossing on foot from Saint-Valéry towards Le Crotoy at low tide, seal-colony walks from the Hourdel lighthouse, bird outings, and themed hikes timed to the grandes marées when the tide comes in across the flats at a walking pace.
The crossing is the signature trip and the one you should not attempt alone — the bay has quicksand, the channels refill fast, and the sandbanks look identical in every direction once you are out on them. That is the actual argument for a guide here rather than an upsell.
They work from the tourist kiosk next to the marina and answer the phone seven days a week. A second number, +33 6 32 70 47 94, covers the same booking line.