Visitors to Lake Washington Ship Canal and Hiram M. Chittenden Locks, Seattle, on Oct. 1, saw an unusual sight: U.S. Army Corps of Engineers employees at the bottom of the small lock chamber using nets to catch fish trapped in the chamber while it was drained for urgent maintenance.
While USACE biologists recovered as many fish as possible, their main goal was to rescue fish listed under the Endangered Species Act (ESA), particularly salmon. At this time of the year, the last Coho salmon of the season make their way through the fish ladder toward their spawning grounds.
Luckily, no salmon or ESA-listed fish were trapped in the locks this time.
“We found primarily sculpin, with a few starry flounder and one gunnel,” said Army Corps Biologist Mary Bacon, Corps biologist.
USACE biologists usually conduct a fish rescue at the small lock every February or March when the locks are closed for routine maintenance, but a leak in the small lock’s gates necessitated another closure this year. When the locks are de-watered, they descend into the lock as soon as it is safe to enter to remove fish.
When drained for maintenance, water levels in the locks drop to a depth of only one to two feet. These low levels do not provide enough oxygen for fish to survive long term, so a timely response is important.
“Because there’s no water coming in, the dissolved oxygen would be used up very quickly by the fish that are still in the water,” said Bacon. “Another thing we consider is temperature. On a warm day, as the water temperature starts to creep up, the dissolved oxygen goes down.”
The work is painstaking—over the course of two days, biologists gently captured scores of small, fast-moving fish hidden among the gravel, shells and debris at the bottom of the lock chamber. After capture, they carefully release the fish into open water outside lock gates.
Past discoveries during fish rescues include a 6-foot white sturgeon, a juvenile harbor seal and even a wedding ring.
The ESA requires the Army Corps to consult with National Oceanic and Atmospheric Administration (NOAA) Fisheries whenever work could potentially jeopardize a threatened or endangered species.
“While the public may see the large-scale operations to maintain and preserve our civil works, there are so many other considerations during operations and maintenance, including the federal responsibility to protect endangered species,” said Bacon.
From engineers, maintenance crews and park rangers, to lock wall crew, biologists and scientists, running the busiest locks in the nation takes a village.