About 2,000 fish have died in Lake Washington near Sound Transit’s new I-90 light rail crossing, and among the carcasses divers found were federally protected Chinook salmon. Amateur divers first spotted a pile of dead fish offshore from Seattle in August 2025, and by summer 2026 they had located nine to 12 separate piles of carcasses beneath the eastbound span near Mercer Island, some resting in water 60 to 180 feet deep.
The die-off has become the subject of an active investigation involving Sound Transit, the Washington Department of Fish and Wildlife, and the National Oceanic and Atmospheric Administration’s Fisheries West Coast Region, according to The Seattle Times, whose reporters Isabella Breda and Mike Lindblom detailed the timeline. Muckleshoot fisheries scientists reviewed images from the die-off and identified at least two Chinook salmon carcasses, with tribal fisheries manager Mike Mahovlich saying that sockeye also appeared to have been killed. “One dead salmon here is bad news,” Mahovlich said, per the same reporting. Most of the dead fish were nonnative species, including smallmouth bass, sculpin and yellow perch identified by a fish and wildlife expert, along with at least one unknown salmonid the expert believed might be a small cutthroat trout.
Anode Cables Under Scrutiny
Investigators are focused on two central questions: how many fish and which species actually died, and whether underwater anode cables carrying stray electrical current are to blame. The I-90 corridor’s cathodic protection system pumps continuous low-level current into the lake through dangling metal anodes designed to divert stray 1,500-volt train current and prevent corrosion of the floating bridge’s concrete pontoons and underwater steel anchor cables, according to reporting compiled by Ground News. Sound Transit spokesperson Tony Raben wrote that some anode strings may have been resting on the lakebed and spaced closer together than intended, and dead-fish piles were found next to hanging anode cables that had become displaced and coiled on the lake bottom.
Sound Transit was notified of the dead fish on August 3, after Washington Department of Fish and Wildlife had already been contacted in late July. The agency issued a corrective-maintenance permit to Sound Transit on August 7, and commercial-diver inspections began August 10 to examine the anode system more closely. On August 23, crews completed an interim fix by lifting 32 underwater anode cables off the lakebed where the dead fish had been concentrated, according to reporting from Kent Reporter. Sound Transit is now inspecting those 32 relocated cables and plans to sample and test fish carcasses this week, while also examining whether a chemical reaction with lake sediment, separate from any electrical cause, might have contributed to the deaths.
A Fragile Salmon Run Already Under Pressure
The stakes extend well beyond one stretch of lakebed. Puget Sound Chinook salmon were listed as threatened under the federal Endangered Species Act back in March 1999, making any unpermitted killing or injury of the species a potential violation of federal law, per NOAA Fisheries. NOAA Fisheries West Coast Region has confirmed that salmonids were affected and said it is awaiting details on the number and species involved, adding that Sound Transit continues to assess and address the problem to prevent further impacts on fish…