Sound Transit Probes 2,000 Lake Washington Fish Deaths Linked to Floating Bridge Electrical System

The Washington State Department of Transportation and Sound Transit have opened an environmental investigation into the deaths of approximately 2,000 fish in Lake Washington near the Interstate 90 floating bridge. The mortality event was first identified in early August when state highway maintenance workers spotted hundreds of dead fish floating near the Mercer Island and Seattle approaches to the Homer M. Hadley Memorial Bridge. Sound Transit officials subsequently confirmed that the deaths appear linked to the bridge's impressed current cathodic protection system. That electrical system was designed to protect the concrete pontoons and internal steel cables from galvanic corrosion caused by the newly opened Link 2 Line light rail service.

Sound Transit Chief Executive Dow Constantine disclosed the preliminary findings during a public Executive Committee meeting, stating that the agency initiated immediate underwater remediation after divers observed localized electrical field concentrations. While investigators determined that the majority of the dead fish were non-native warm-water species, biologists confirmed that migrating salmon were also found among the losses. Sound Transit and state transit leaders maintain that passenger train service and vehicular highway lanes remain structurally sound and safe for daily operations across Lake Washington.

Maintenance Crews Discover Thousands of Dead Fish Near Floating Pontoons

State transportation maintenance personnel first spotted dead fish drifting in Lake Washington on August 3, 2026. Routine environmental monitoring along the Interstate 90 corridor quickly revealed that fish carcasses were accumulating specifically around the western and eastern anchor spans of the Homer M. Hadley Memorial Bridge. As reported by KOMO News, bridge inspection teams notified regional environmental officers after observing recurring clusters of deceased fish along the lake surface and near shoreline rocks.

Initial estimates gathered by agency biologists placed the total mortality at approximately 2,000 fish over a multi-week span. Field personnel reported that yellow perch and smallmouth bass accounted for the largest volume of casualties. Both species commonly inhabit the vegetated nearshore shallows where water depth drops gradually toward the deep central lake trench. However, tissue examinations also identified a smaller number of juvenile salmonids that were navigating the lake corridor toward Puget Sound.

According to coverage by Lynnwood Times, the spatial concentration of dead fish was tightly confined to zones directly adjacent to specific bridge anchor points rather than dispersed widely across the open lake basin. Water chemistry sampling conducted within twenty-four hours of the initial alert confirmed normal dissolved oxygen levels, neutral acidity, and the absence of petroleum or toxic chemical discharges. That environmental baseline pointed investigators away from water contamination and toward electrical energy fields generated beneath the water surface.

How Cathodic Protection Systems Function in Freshwater Lakebeds

The Homer M. Hadley Memorial Bridge carries four highway lanes and dual light rail tracks atop twenty-two hollow concrete pontoons. When Sound Transit constructed the East Link light rail extension across the structure, engineers faced unprecedented electrical challenges. Passenger trains operate on high-voltage direct current supplied through overhead catenary systems. Return current travels along the steel running rails, creating risks of stray direct current entering the lake water or penetrating the bridge structure. Stray direct currents accelerate galvanic corrosion on underwater steel cables, post-tensioned rods, and steel rebar inside concrete pontoons.

To neutralize that corrosive threat, transportation engineers installed an impressed current cathodic protection system. The installation utilizes strings of specialized anodes suspended into the lake water alongside the floating pontoons. By delivering controlled electrical current through the anode strings, the system renders the bridge metal cathodically polarized, forcing the sacrificial anodes to absorb oxidation instead of the bridge structure. As reported by MyNorthwest, engineers designed the system to emit low-voltage currents that typically dissipate harmlessly in open freshwater.

Trouble arose when thirty-two individual anode strings drifted from their intended vertical suspensions and rested directly against the muddy lakebed in shallow water. In deep water, electrical current diffuses uniformly into the surrounding water column. When the anode assemblies contacted sediment in shallow margins, they created concentrated electrical voltage gradients. Fish entering these high-density zones suffered involuntary muscle contractions, physical disorientation, and respiratory failure caused by galvanic electrical field exposure.

Tribal Biologists and State Agencies Assess Salmon Run Risks

The mortality findings prompted immediate mobilization among tribal fisheries managers, state biologists, and federal wildlife authorities. The Muckleshoot Indian Tribe and Snoqualmie Tribe retain treaty-protected usual and accustomed fishing rights throughout the Lake Washington watershed, which serves as the primary migratory highway for Cedar River sockeye, Chinook, and coho salmon. Tribal biologists launched joint surveys with the Washington Department of Fish and Wildlife to determine whether the electrical field created an impassable barrier for migrating fish stocks.

Juvenile salmonids leaving the Cedar River and Sammamish River must transit Lake Washington before reaching the Ballard Locks and entering Puget Sound. During late summer, high surface water temperatures often force young salmon toward cooler nearshore depths, bringing them into potential proximity with bridge approach structures. Tribal resource managers expressed acute concern that even non-lethal electrical fields could disrupt natural migratory navigation or stun fish, making them vulnerable to predatory birds and invasive northern pike minnow.

Federal regulators from the National Oceanic and Atmospheric Administration Fisheries division and the United States Army Corps of Engineers have requested comprehensive telemetry data from Sound Transit. Biologists are collecting tissue samples from recovered salmon carcasses to verify whether electroshock trauma or secondary physical injury caused each fatality. Fisheries leaders stressed that protecting fragile Puget Sound salmon runs requires strict regulatory compliance, particularly given the millions of dollars invested annually by regional taxpayers in habitat restoration projects across western Washington.

Emergency Dive Teams Reposition Suspended Anode Cables

Sound Transit mobilized commercial contract dive teams within days of receiving the WSDOT notification to survey underwater conditions beneath the Homer M. Hadley Memorial Bridge. Divers equipped with specialized underwater video cameras and acoustic sensors performed detailed inspections along the entire length of the floating alignment. As confirmed by KING 5, divers identified thirty-two anode cables that had accumulated heavy sediment or settled directly onto the bottom substrate near both Mercer Island and Seattle shores.

Between August 15 and August 23, 2026, marine contractors executed an emergency remediation protocol under joint agency oversight. Working from support barges positioned beneath the highway deck, technical crews raised every grounded anode cable off the lakebed. Technicians secured the anode strings with new non-conductive tension rigging, suspending them at least six feet above the sediment layer to ensure unimpeded water circulation around each electrical element while recalibrating onshore electrical rectifiers.

Subsequent underwater voltage measurements demonstrated an immediate reduction in electrical field intensity along the lakebed contours. Sound Transit environmental monitors reported that new fish mortalities dropped to zero following the completion of the cable lifting operations on August 23. The agency stationed dedicated observation vessels near the bridge approaches to conduct daily carcass counts and verify water clarity. Engineers are now drafting long-term anchor modifications, including rigid fiberglass spacing conduits, to prevent seasonal wave action or winter lake currents from pushing cables back toward the bottom.

Engineering Legacy and Stray Current Challenges on Interstate 90

The Homer M. Hadley Memorial Bridge opened in 1989 as a highway crossing and was retrofitted over a decade of complex construction to accommodate heavy passenger rail vehicles. Operating sixty-ton electric trains across a buoyant concrete roadway represents a world-first engineering endeavor. Concrete floating bridges rely on balanced buoyancy, flexible expansion joints, and tensioned steel anchor cables embedded in the lake floor. If stray direct current from train motors reaches steel tendons, hydrogen embrittlement or rapid electrochemical rust can compromise structural integrity.

To address that hazard, project planners developed a multi-layered stray current mitigation strategy during the East Link design phase. The original design called for electrical isolation pads beneath running rails, stray current collection mats, and the impressed current cathodic protection network. However, public records indicate that testing protocols focused predominantly on structural preservation and current collection efficiency rather than ecological field interactions in shallow nearshore zones.

Independent transit analysts note that operating light rail in a freshwater environment presents different physics than marine saltwater environments. Freshwater possesses significantly lower electrical conductivity than ocean water, meaning higher voltage differentials can form over shorter distances between anodes and grounding points. While cathodic protection systems operate safely on maritime shipping piers and oil platforms worldwide, balancing electrical corrosion control with freshwater aquatic safety requires constant monitoring that public transit agencies rarely encounter on terrestrial rail lines.

Regional Transit Operations Continue Amid Environmental Oversight

Despite the environmental concerns raised by the fish mortality event, Sound Transit and the Washington State Department of Transportation emphasized that public transit service remains unaffected. Trains continue operating across the 2 Line corridor between Seattle, Mercer Island, Bellevue, and Redmond, carrying tens of thousands of weekday commuters across Lake Washington. WSDOT Secretary Julie Meredith and agency safety directors confirmed that bridge structural monitoring sensors show no electrical hazards to train passengers, automobile drivers, or pedestrian trail users.

The agency has committed to delivering a comprehensive environmental audit to the Sound Transit Board of Directors and the Washington State Department of Ecology before the end of September. The audit will examine whether initial design specifications failed to account for cable slack and sediment accumulation in shallow water zones. State lawmakers on transportation committees have signaled that they will review the findings during upcoming legislative committee hearings in Olympia, seeking assurances that future light rail expansions do not harm local aquatic ecosystems.

For Puget Sound transit patrons and environmental advocates, the incident highlights the complex balance between expanding mass transit infrastructure and safeguarding regional natural resources. Long-term solutions under consideration include relocating anode arrays to deeper mid-lake waters, adjusting rectifier power outputs during peak salmon migration windows, and installing permanent underwater field sensors. Until permanent engineering designs receive interagency approval, Sound Transit will maintain weekly dive inspections and continuous electrical field monitoring along both shores of Lake Washington.