Some coho salmon migrate a considerable distance into Interior rivers to spawn. Coho salmon in the Yukon River drainage have been found spawning near Old Crow on the Porcupine River- almost 2,000 miles from the sea. Most spawning streams are narrow and shallow with a gravel substrate. Coho salmon also seem to favor streams with an upwelling of ground water. The female digs a redd, consisting of several pits, and deposits her eggs in the stream gravels.
Alaskan coho salmon live in streams for at least a year before migrating to the sea.
The small fish choose quiet backwaters and side channels with overhanging vegetation when they first emerge from the redd. As they grow, coho salmon fry move into more open, higher velocity water. Streams with a complex structure of boulders, logs, and brush in the water can support the most coho salmon fry. The small fish defend these territories aggressively. Juvenile coho salmon occupy different stream habitats in the fall and winter.