For young salmon and steelhead in the Lake Washington watershed, there is only one way to get to sea: through the Ballard Locks.
This week, the U.S. Army Corps of Engineers will be installing smolt flumes to help juvenile fish pass safely through the spillway gates. The annual flume installation is just one step the Army Corps has taken to improve salmon survival rates in the recent years.
Marian Valentine, who directs operations at the Locks for the Army Corps, said studies in the 1990s found that the Locks were adding another level of danger to the already-perilous journey to sea for young salmon.
"You have to get a lot of smolts through to get an adult salmon back," Valentine said.
Two decades ago, juvenile salmon and steelhead were having a hard time making it over the Locks spillway. Others were getting pulled into filling culverts: big tunnels that could lead them through the Locks. However, the culvert walls were caked with barnacles, sharp enough to hurt or kill smolts.
Now, every spring, the Army Corps installs funnel-like structures in the spillway gates called smolt flumes.
"They’re sort of like slides, smolt slides, to give them a quick ride out of the system and get them out to sea," Valentine said.
Along with putting in flumes, Valentine said, workers now also scrape all of the barnacles off the culverts once a year "so that it’s a smoother surface for the smolts to pass, so they don’t get scraped up and kind of a ground up in [the culverts]."
In addition, the spillway is kept open later in the summer to let more smolts through.
Valentine said about 200,000 sockeye salmon, the first to return from the sea, came back through the Locks last year.
The fish ladder at the Locks will open in time for Memorial Day weekend.