What killed all the fish under the I-90 floating bridge? What we know

SEATTLE - Dead salmon and other fish discovered beneath the I-90 floating bridge in Lake Washington have prompted an investigation into what killed them and whether equipment designed to protect the bridge from corrosion played a role.

Diver Travis Eiler said he encountered piles of dead fish about 80 feet below the surface, near lines extending down from the bridge pontoons.

Sound Transit says the lines are anode strings, part of a system designed to protect the structure from corrosion. The agency has since lifted the cables off the lakebed as it works to determine what caused the fish deaths.

Diver discovers piles of dead fish

Eiler was exploring the ruins of the old I-90 floating bridge when he encountered the fish.

"At first I thought it was maybe a science experiment," recalled Eiler.

He described seeing "piles of dead fish with these lines coming down from the bridge leading to them."

What particularly struck Eiler was that the dead fish did not appear to be getting eaten. When he returned about a week later, he said the decaying fish were still there and he could see fresh kills.

"They stayed there intact for so long," he remarked. "They actually started growing a fur, like a fungus, on them."

Eiler said he and others initially did not know who to alert, but knew something appeared to be wrong. They began contacting conservationists as well as the Washington Department of Natural Resources, Washington Department of Fish and Wildlife and Muckleshoot tribes.

Attention turns to anode strings

Eiler said hundreds of lines extend down from the bridge pontoons and are designed to protect the structure from corrosion.

"They were actually down in the bottom in the silt," he said. "We don’t think it's electrocuting them, but it might be creating some type of chlorine gas or something."

Eiler told FOX 13 Seattle he thinks the lines could potentially be stunning the fish.

Sound Transit identified the equipment as anode strings. The agency said it was alerted by its partners at the Washington State Department of Transportation on Aug. 3 about deceased fish near the strings.

"We take this matter very seriously and acted as soon as we were made aware of the issue," Sound Transit said in a statement.

The agency has since removed the anode strings from the lakebed.

Sound Transit investigates cause

Sound Transit said divers are inspecting the locations where the anode strings were removed to determine whether there are any recent signs of fish mortality.

The agency is also developing a sampling and testing plan with Tribal fisheries managers and other regulatory agencies.

Eiler said the response came quickly once the issue reached officials.

"They had divers in the water within days," he said.

When Eiler returned to the area this week, he said he saw a potentially positive sign.

"We’ve since noticed that there is no fresh fish at the bottoms of those lines," said Eiler.

The cause of the fish deaths, however, has not yet been determined.

Sound Transit said it hopes testing over the next several weeks will identify the root cause and allow the agency to begin implementing a long-term solution.

The agency said it believes it has mitigated the immediate issue by lifting the anode cables off the lakebed.

Sound Transit told FOX 13 Seattle it is exploring switching to a closely coupled anode system, similar to the cathodic protection system used on the SR-520 floating bridge.

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