Redd
A shallow nest a female salmon or trout digs in river gravel with her tail to lay her eggs.
Also: spawning nest
A female salmon or trout turns on her side and beats her tail against the gravel of a stream, lifting stones and clearing a shallow pit. She lays eggs in it, a male fertilises them, and she covers them with gravel from just upstream. The eggs stay among the stones, where water flows through and keeps them supplied with oxygen, until they hatch. Silt from logging, farming or construction can smother redds, which is one reason clean, gravel-bedded rivers matter for these fish.