After 1 to 7 years in the ocean, the adult salmon that have survived countless hazards from predators, ocean conditions, and commercial harvest return to the Columbia River and head for their home streams.

Five to 10 percent of adults die in each of the 8 or 9 dams they must pass to reach their destination.

Arriving at her home stream, a female builds a nest, or redd, in fine, clean gravel.

As a female deposits her thousands of eggs, a male releases milt, fertilizing them. Both male and female salmon die soon after spawning, except steelhead and cutthroat, which may survive another year or more to spawn again.

Tiny yolk-sac fry, or alevins, hatch after 2 to 8 months. They stay in the gravel for another1 to 3 months until the nourishment from the yolk sac is used up. They need cold, pure water to aerate the gravel and wash away their wastes.

The fry emerge from the gravel and begin to feed on their own. Many are lost to predation, competition, or failure to adapt to stream conditions. Some types of salmon begin their migration downstream soon after emergence, while others stay in freshwater for a year or more.

During migration the fry are vulnerable to predators, such as birds or northern pikeminnow, walleye, and bass, which thrive in the reservoirs. Seven to 15 percent die passing each dam.

By the time they reach the estuary, the fry have become smolts, and are adapting phsiologically to saltwater. Here they linger to feed and grow before entering the ocean. Predators, unfavorable conditions, and failure to adapt will deplete their numbers further.