An estimated 2,000 fish, mostly non-native species, have died near the bridge. Exact counts are difficult, in part because many have decomposed, transit staff said. Sound Transit for months has hailed its innovative engineering to control electric current over the lake, so news that fish are being killed comes as a letdown.

The Washington State Department of Transportation discovered the problem Aug. 3 and notified Sound Transit promptly, according to transit CEO Dow Constantine.

“We are still in the discovery mode. Fish biologists and engineers are now busy analyzing photos and video collected by the divers,” Constantine told a transit-board committee. “Early analysis has shown that the majority of fish are non-native or invasive perch and bass, with a small number of salmon identified.”

The dead fish were clustered near the ends of the bridge, where cables to control electric current rested on the lake bottom, Constantine said.

WSDOT Secretary Julie Meredith, speaking remotely at Thursday’s meeting, said officials are working to find the cause, and are coordinating with environmental agencies, as well as tribes that monitor fish runs.

“The bridge remains safe for the traveling public, and WSDOT and Sound Transit are going to continue to share the responsibility for guaranteeing that, both now and over the long term,” she said.

The light rail tracks, where train service began March 28, run next to the westbound lanes of I-90. The water closest to the trains — between the westbound Hadley bridge and the nearby eastbound bridge — is a maintenance zone where the public doesn’t boat, swim or kayak.

Regardless, transit staff say electric current next to floating bridges isn’t powerful enough to harm someone in the water. Scuba diving to visit old sunken I-90 pontoons is “relatively popular,” said WSDOT communications director Ryan Overton. The eastbound bridge, even without trains, also has cables where low-level current travels, “and they are not a health hazard,” he said.