In late October and early November, decreasing day length and cool water temperatures stimulate spawning activity. The tail end of a pool seems to be a preferred salmon spawning area. Still water, or stream bottoms of sand, silt, or mud, would smother the eggs. The fertilized eggs are covered with gravel when the female moves substrate material upstream from the redd. During the spawning period, a female may dig more than one redd, depending on the size, and the clean mound of gravel with its upstream depression makes it clearly visible.
Some mounds contain no eggs and are referred to as test redds, false redds, or scrapes.
The female salmon provides about 1,500 eggs per kilogram of body weight. After spawning, spent adults, known as kelts, usually remain in deep pools over winter and return to the sea in Spring. These fish are in poor shape, and their skinny, dark appearance has given rise to the terms, slinks or black salmon. The pale orange eggs measure about 6 mm in diameter, by January, the eyes of the developing fish are visible. The delicate alevin measures 15 mm in length and is normally found buried in the gravel, absorbing nourishment from its attached yolk sac for a period of 2-5 weeks.