The world's first light rail line over a floating bridge is inadvertently killing fish in Lake Washington, and now Sound Transit is scrambling to for a solution
The world's first light rail line over a floating bridge is inadvertently killing fish in Lake Washington, and now Sound Transit is scrambling to find a solution.
It's unclear how many fish have died and how long the problem has existed since the Crosslake Connection first opened on March 28, linking Seattle to the Eastside along the I-90 floating bridge.
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Sound Transit learned about the issue earlier this month.
"On August 3, we were alerted by our partners at the Washington State Department of Transportation to some number of deceased fish in the vicinity of the I-90 floating bridge," said Sound Transit CEO Dow Constantine on Thursday.
A diver noticed the dead fish and alerted authorities. Sound Transit responded by sending its own dive teams, as well as fish biologists and engineers, to see first-hand what was going on. Constantine said they also contacted the appropriate regulatory agencies and Tribal fisheries managers.
"That work identified a potential connection or correlation between fish mortality and localized portions of the bridge's cathodic protection system," Constantine said, "particularly towards the ends of bridges where the strings of anodes were clustered and actually resting on the lake bed."
These strings are part of the cathodic protection system that manages low-level electrical current from the bridge and the light rail system.
A cathodic protection system prevents metal structures from corroding with rust by making the protected metal act as a cathode in an electrical circuit.
A decision was made to lift those strings off the bottom of the lake bed and suspend them in the water, which was completed on Aug. 23, some 20 days after Sound Transit learned of the problem. However, it's unclear if this mitigation measure has resolved the problem or if fish near the floating bridge continue to be killed or are at risk.
"We are still in the discovery mode," Constantine said.
Fish biologists and engineers are now analyzing photos taken by the dive teams. Initial findings show that the majority of the dead fish are "non-native or invasive perch or bass," Constantine said, though a number of salmon have been identified as well.
Washington State Secretary of Transportation Julie Meredith said her agency is taking the issue very seriously as they work to understand the root cause and develop a long-term fix. She emphasized that the crossing poses no risk to the public.
"The bridge remains safe, safe for the traveling public," Meredith said. "WSDOT and Sound Transit are going to continue to share the responsibility for guaranteeing that."
The Crosslake Connection opened after a long period of planning, advocacy, and engineering. Efforts to design a mass transit system connecting Seattle and Bellevue date back to the 1960s, when plans for a regional rapid transit system were included in a group of ballot initiatives called Forward Thrust.
The engineering required to put fixed rails on a floating bridge is complex and extensive. Sound Transit had to invent new track bridges and solve the question of how to protect a floating concrete structure from stray electrical current. The transit agency said the electrical management system they have has been widely tested and is used both locally and throughout the world on bridges with no adverse impacts on fish.
Monitoring and analysis is ongoing.
"We are committed to ensuring that the long-term solution is effective and monitored on an ongoing basis," Constantine said.
