Seattle’s new I-90 light rail opened in March; 5 months later, about 2,000 fish have died near electrical equipment in Lake Washington

When Seattle’s new light rail service began running across Lake Washington in March 2026, it marked a major milestone for the region’s public transportation system.

But within weeks, maintenance crews and boaters began noticing something unusual in the water below the I-90 floating bridge: dead fish.

By late summer, roughly 2,000 fish deaths had been reported near the bridge, prompting Sound Transit, the Washington Department of Fish and Wildlife and other agencies to investigate whether the newly installed electrical infrastructure could be harming aquatic life.


The investigation is still underway, and officials have not yet established exactly what is killing the fish. But the location of the deaths — concentrated around portions of the new rail system that extend into Lake Washington — has raised questions about whether energized equipment or electrical fields could be involved.

Why are fish dying near the I-90 bridge?

The I-90 floating bridge already carried Interstate 90 across Lake Washington. Adding light rail required an extensive new electrical and structural system capable of powering trains as they travel across the floating span.

Some of that infrastructure extends below the bridge deck and into the lake.

That makes the situation unusual. Instead of a conventional rail line on solid ground, Sound Transit had to install electrical components in and around a major body of water that supports fish, wildlife, boating and other recreational activities.

Reports of dead fish began appearing shortly after rail operations started.

Many were found floating in the water or washed toward shore near sections of the bridge where electrical cables and related equipment are located. The geographic concentration has made the transit infrastructure a major focus of the investigation.

The electrical-field question

One possibility being examined is relatively straightforward: fish could be coming into contact with energized equipment or electrical currents escaping from components that were supposed to be insulated.

But investigators are also considering less obvious mechanisms.

Electrical systems can produce electromagnetic fields, and researchers are examining whether those fields could be affecting fish behavior or physiology in the area.

Depending on the eventual findings, possibilities could include direct electrical injury, muscle spasms, disorientation or other forms of physiological stress.

At this stage, however, it is important to distinguish a suspected connection from a confirmed cause. Fish kills can have many explanations, including disease, changes in water conditions and other environmental factors. Investigators are therefore examining affected fish and the bridge's electrical systems to determine precisely what happened.

Why Lake Washington matters

The incident is significant because Lake Washington is not simply the backdrop for Seattle's transportation network.

It is a functioning aquatic ecosystem supporting multiple fish species and the wildlife that depends on them. The lake is also heavily used by boaters, anglers and other recreational users.

A localized fish kill involving thousands of animals can therefore raise concerns beyond the immediate loss of fish.

Smaller fish form part of the food supply for larger fish, birds and other predators. A sustained mortality event could potentially affect portions of the local food web, although the broader ecological consequences will depend on the scale and duration of the problem.

There is also a highly visible human dimension.

Dead fish accumulating around a major public infrastructure project can quickly become a symbol of an unintended environmental cost — particularly when the project itself was intended to provide a cleaner alternative to automobile travel.

What is Sound Transit doing?

Sound Transit has acknowledged the fish deaths and is working with state and federal agencies to identify the cause.

Investigators are examining the underwater electrical equipment for possible faults, exposed components, insulation problems or inadequate shielding. Fish mortality is also being monitored to determine whether deaths continue and whether they remain concentrated around particular sections of the bridge.

Biologists can examine affected fish for signs of electrical injury while investigators assess other possible explanations, including disease or environmental conditions.

If the investigation determines that the rail equipment is responsible, officials could require modifications to the system. Depending on the severity of the problem, certain equipment could potentially need to be repaired, redesigned or temporarily taken out of service.

What could fix the problem?

Several possible solutions could be considered if an electrical cause is confirmed.

Additional insulation or shielding could prevent electrical currents from reaching the surrounding water. Underwater components could potentially be redesigned or relocated to reduce their interaction with fish.

Physical barriers might also be used to keep fish away from particular pieces of equipment.

Another possibility could involve operational changes, although any adjustment to electrical power would have to maintain the safety and reliability of the rail system.

None of these options is necessarily simple.

Retrofitting infrastructure on a floating bridge can be expensive and technically difficult. Additional structures could interfere with water movement or create new problems for wildlife and boaters. Any modification would also need to be tested carefully before being deployed.

A lesson for future infrastructure projects

The Lake Washington fish deaths illustrate a broader problem faced by modern infrastructure: a project can satisfy its engineering requirements while still producing consequences that were difficult to predict beforehand.

Floating bridges and underwater electrical systems operate in an environment that is constantly changing.

Fish move differently at different times of year. Water currents shift. Equipment ages. Small electrical faults can emerge only after a system has been operating for months. And wildlife does not necessarily behave the way engineers expect it to in planning models.

That makes post-construction monitoring particularly important for projects built in sensitive ecosystems.

The I-90 incident could eventually influence how underwater electrical systems are designed, insulated and monitored on future transit projects.

It could also lead to more extensive environmental monitoring after major infrastructure projects become operational, rather than relying primarily on predictions made before construction.

Can Seattle's transit goals and environmental protection coexist?

The light rail expansion represents a major investment in the Seattle region's transportation future. Moving more people by rail can reduce dependence on cars and support broader efforts to build a more sustainable transportation network.

Lake Washington represents a different kind of regional asset — one that cannot simply be redesigned if something goes wrong.

That tension makes the fish deaths particularly consequential.

The immediate question is straightforward: what is killing the fish?

The longer-term question is harder.

If the new infrastructure is responsible, Sound Transit and regulators will have to demonstrate that the problem can be fixed without compromising the rail system — and that environmental safeguards are strong enough to prevent similar problems in the future.

For now, the investigation continues. The roughly 2,000 reported fish deaths are a troubling reminder that even ambitious infrastructure designed with sustainability in mind can have unexpected effects once it meets the real-world environment.

The eventual findings could determine not only what happens beneath the I-90 bridge, but also how future transportation projects are designed where modern infrastructure and fragile aquatic ecosystems have to share the same space.