Caddisflies
Gammarids
The Yères is the quietest of the Seine-Maritime chalk streams, running for sixty-odd kilometres from its rise near Fresnoy-Folny down to the sea at Criel-sur-Mer. It's pure chalk — clear, cold, stable, slightly less buffered than the bigger Normandy rivers but still running within five or six degrees of its annual mean — and it holds wild brown trout throughout, with grayling in the better pools below Sept-Meules. Not a river of monsters. The average fish is modest and the technique is classic: small flies, fine tippets, long leaders, patience. Mayfly through the third week of May, sedges through June, and blue-winged olives into September. AAPPMA access for most of the length. A good choice when the Arques or the Bresle are too crowded and you want a quiet day on water that rewards knowing how to read it.
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