Damaged Spawning Grounds
When the salmon are ready to spawn, they search for gravel to build their nests in. Often the gravel is either buried under fine sediment from landslides from deforested areas upstream, or scoured away by too-high stream velocities caused by straightening of the river channel, diking and hardening the riverbanks, loss of large woody debris that roughens the channel and slows the water, and other human activities. Also, the water covering the gravel must not be too deep, too shallow, or too fast.
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