Colors of spawning chinook salmon in fresh water range from red to copper to almost black, depending on location and degree of maturation. Juveniles in fresh water are recognized by well-developed parr marks which are bisected by the lateral line. They hatch in fresh water, spend part of their life in the ocean, and then spawn in fresh water. All chinooks die after spawning. Chinook salmon may become sexually mature from their second through seventh year, and as a result, fish in any spawning run may vary greatly in size.
Females tend to be older than males at maturity.
Alaska streams normally receive a single run of chinook salmon in the period from May through July. Chinook salmon often make extensive freshwater spawning migrations to reach their home streams on some of the larger river systems. Yukon River spawners bound for the extreme headwaters in Yukon Territory, Canada, will travel more than 2,000 river miles during a 60-day period. Chinook salmon do not feed during the freshwater spawning migration, so their condition deteriorates gradually during the spawning run as they use stored body materials for energy and for the development of reproductive products. Each female deposits from 3,000 to 14,000 eggs in several gravel nests, or redds, which she excavates in relatively deep, moving water.