A later addition to the dam is this fish ladder, consisting of 48 steps, or pools, by which the fish are able to navigate the 50 feet from the river below the dam to the top of the dam.
How it Works
1 • Designing and positioning a fish ladder so fish can find and use it is a challenge—it's not like you can put up a sign pointing the way. Migrating fish are attracted by current and can be coaxed to certain areas by manipulating water flow. To lure fish to the ladder, flow up to 80 cubic feet per second (cfs) is discharged in front of its entrance pool.
2 • Once inside the ladder, fish swim from pool-to-pool against a 6 cfs flow. Pools are about 5 feet wide and 6 to 10 feet long, and the total length of the ladder is 356 feet. The ladder was designed to assist fish migrating upriver—fish traveling downstream pass over the dam or through the powerhouse.
3 • Near the top of the ladder is an area that can be used to trap and hold fish, so biologists can count, sort, tag, and measure them. Some fish may be selected for truck transport to upstream locations. But biologists don't need to be here to monitor fish activity—some fish using the ladder will be carrying tags that can be read by a nearby antenna, enabling biologists to automatically record their passage.
4 • Fish exit the ladder to the reservoir through a 3-foot-wide tunnel in the dam, near its crest. Most fish using the ladder are traveling to their natal spawning areas, which are upstream from here. Look for bull trout mostly in the spring and fall; cutthroat trout, rainbow trout, northern pikeminnow, peamouth and suckers mainly in the spring; and brown trout and mountain whitefish mostly during late summer and the fall.
From the plaque at the fish ladder