Chalk stream

[c] The beds of the rivers are generally composed of clean, compacted gravel and flints, which are good spawning areas for Salmonidae fish species.

[3] Since they are fed primarily by aquifers, the flow rate, mineral content and temperature range of chalk streams exhibit less seasonal variation than other rivers.

[3] In addition to algae and diatoms, the streams provide a suitable habitat for macrophytes (including water crowfoot)[6] and oxygen levels are generally supportive of coarse fish populations.

Chalk streams transport little suspended material (unlike most rivers), but are considered "mineral-rich" due to the dissolved calcium and carbonate ions.

The unique characteristics of chalk stream ecology are due to stable temperature and flow regimes combined with highly transparent water and lack of sand grade sediment particles.

The rich invertebrate life and characteristic transparent shallow water make chalk rivers and streams particularly suited to fly fishing.