Stoneflies
It is a river of two characters. The upper section, above L'Isle-sur-Serein, is small and limestone-influenced, picking up character as springs feed into it from the Jurassic flank. The middle reach, through the Chablis vineyards, is the river most anglers think of: slower, greener, heavier with weed in summer, carrying the particular stability that comes from groundwater buffering. Fish the upper and middle reaches for wild brown trout. The hatches are good — Baetis throughout the season, grannom caddis in April, olives building into May, and the usual terrestrial opportunities once the meadow flies start dropping in June. Grayling are present but patchy. The Serein responds slowly to rain because the limestone aquifer absorbs and releases water gradually, which means the river is rarely out of fishable condition for long. Start with a size 16 olive nymph in the morning and expect to be fishing dry fly by midday if the weather is kind.
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.
- Limestone