In Sonoma County, California, a new fish ladder has been installed for Coho salmon, in an attempt to entice them further upstream and back to their natural spawning grounds, which they have been unable to reach for over a decade. The new fish ladder is part of a multi-billion dollar project to improve the river systems and habitat for Coho salmon, a project that has been going on for more than twenty years. The new development is based in Purrington Creek, which is unusual because the water flows there all year round (many of California's smaller waterways are dry during the summer months). At the creek there is a concrete culvert that diverts the natural water path and makes it impassable to Coho salmon, who need at least a foot of water to swim in if they are to make the jumps upstream. The fish ladder is a slot and dam type, with four concrete dams with a niche in the middle that allows the water to flow through steadily. Behind each dam is a pool where the salmon can rest before making the jump to the next section and eventually past the obstacle. The extra space that the salmon can reach totals 4,700 feet of potential gravel bed spawning grounds and is expected to help raise the spawning numbers back to at least the levels of the 1990s, where 5,000 Coho spawned in Northern Californian rivers. In the 1940s, before the construction of the obstacles that rendered the normal spawning grounds unreachable, the figure was closer to 50,000. Steelhead trout also spawn in the same areas, and they have been spotted upstream from the culvert. Steelhead can jump higher and swim faster than salmon, so they have not been so badly affected by the building of the culvert.
The New Ladder
Purrington Creek runs onto Green Valley Creek, which is one of the last waterways in the Russian River watershed that is known to support a large Coho population. For this reason, and the fact that is runs all year round, Purrington seemed to be the perfect location for a new salmon ladder. However, it took several years to secure the funding for the project, despite the creek being on a short list of problems to address. The new fish ladder may look quite basic, but cost just under $400,000 to build. The project engineers would have preferred to make a more natural looking ladder by setting boulders into the stream, but this would have meant cutting down a lot of trees. As it is, project teams plan to plant willow in the areas around the fish ladder to provide shade and keep the water cool for the Coho. During the construction of the fish ladder, fish were removed from the creek and a pipe was used to divert the flow of water around the building site. At the present moment there is not enough water in the system for the Coho salmon to swim anywhere, but those involved in the project are hopeful that the next big surge of water will entice them to explore upstream. Juvenile Coho salmon stay in fresh water for their first year, after which they are read to spend a year or two at sea before returning to spawn. Coho die after laying and fertilising their eggs, so it is important that the waterway is passable to juveniles so they can find the good spawning grounds before they need to use them. Further phases of the Californian project will see more fish ladders being built and improved to help all species of fish make use of their natural habitats again.