Stoneflies
Gammarids
It rises out of the Artois chalk above Fressin and runs roughly northwest to Étaples, picking up the Course and the Ternoise on the way and gaining in character with every tributary. The water is clear, heavily watercressed, cool in summer — proper chalk stream water that surprises anglers who think of Picardy as flat arable country. Wild brown trout through the middle reaches, grayling in the bigger pools, and sea trout running in from Étaples when the water has colour. Mayfly hatches around Brimeux in May, sedges through the long evenings of June. The beats around Hesdin and Montreuil-sur-Mer are classic — AAPPMA and private estate water mixed together — and the fishing rewards people who'd rather watch for twenty minutes before tying on.
In chalk-spring and karst trout systems, generally stable temperatures broaden olive and other mayfly activity from early spring into autumn, with strong evening caddis, steady subsurface scuds and buzzers where clear groundwater and weedbeds develop, and terrestrials from meadow and woodland banks rounding out the food calendar, depending on how fast each river drops and clears after rain.
- Chalk