Chalk stream fly fishing

A chalk stream starts as rain falling on chalk hills. The chalk filters it slowly underground before it emerges as a spring, which is why the water runs clear and stays close to the same temperature all year, cool in summer and mild in winter. That stability is unusual: most rivers rise and fall with the weather, but a chalk stream barely reacts to a single rainy or dry week.

The steady flow and temperature let weed grow thick through the summer, and the weed holds an unusually rich head of insect life, which is what draws wild brown trout and grayling and makes dry-fly fishing so productive on rivers like the Test and the Itchen. Chalk streams are also rare: the geology that makes them only occurs in a handful of places worldwide, and most of it is in southern England.