SUBSTRATE

STREAM SUBSTRATE

A healthy stream bed consists of three sizes of rocks which keep the water flow steady:

In general, boulders are about the size of a football or larger, cobble is similar to a grapefruit, and gravel can be anything similar in size to jumbo marbles or smaller. Two other types of stream bed material are bedrock and fines. Bedrock is very solid ground and cannot wash away, unlike fines, which are very small rocks, silts, clay, and dirt. They often wash downstream when waters move fast.

All stream substrates are important,
but salmon will only lay their eggs in gravel.

Salmon dig nests in gravel areas in order to lay their eggs. The gravel must be small enough to allow the female adult to dig the nests with her tail, up to 20cm - 30cm deep, and to cover up eggs after they are fertilized.

Different salmon prefer different sizes of gravel. Some bury their eggs deeper than others, while some dig nests larger then others. But all salmon need clean gravel to spawn in and reproduce!