In 1948, America built Mud Mountain Dam for flood control; decades later, a $112 million facility was designed to carry 1.2 million fish around it annually

For much of the 20th century, American engineers built large dams to control rivers and protect growing communities from floods. The Mud Mountain Dam in Washington State is one example of how those decisions played out over time, and of the tradeoffs that came with them.

The dam was completed in 1948 to prevent flooding downstream communities, but it cut off salmon migrations. The U.S. Army Corps of Engineers later spent $112 million on what is billed as the nation's largest trap-and-haul fish passage facility, able to transport up to 1.2 million fish per year. The project aimed to balance public safety and environmental considerations, as reported in the 2018 press release from the Corps. It's a tale of shifting priorities in America as much as it's a tale of engineering.

A dam born from disaster


Mud Mountain Dam is located on the White River in Washington, upstream of Enumclaw, and it keeps the river from seasonally flooding communities all the way to Tacoma. The rock-filled, earthen dam was constructed by the Army Corps following years of catastrophic floods and not just to harness electricity. Its goal was simply to provide a temporary water barrier and to save lives, homes, and businesses.

It has accomplished just that. According to the 2005 Corps report, the project is one of the most valuable systems for flood risk management in the White and Puyallup River valleys today and protects over 400,000 homes and businesses. However, rivers don't only serve one purpose. It was flood control for humans, but a wall for the salmon.

Salmon didn't read the blueprint

Migration isn't a trip for Pacific Northwest salmon; it's a millennia-old instinct. Each year Chinook, steelhead, and bull trout run upstream to spawn, sometimes to go back to their place of birth. That ancient route was cut off by the construction of Mud Mountain Dam. The engineers predicted this problem before the dam's construction. The dam had a trap and haul facility built in 1941, which was an innovative solution for the time to capture migrating fish below the dam and truck them up to the hatchery.

There was the problem of scale, however. The system was built to transport 20,000 fish per year, but eventually it was used on several occasions, for instance during the peak of the pink salmon run, for the same number of fish astonishingly in a day. Several populations of salmon, as well, were listed under the Endangered Species Act, making it difficult to uphold conservation standards for the species in the modern era.

A $112 million engineering rethink

Instead of eliminating the dam (which is being widely considered in other parts of the U.S.), the Corps opted for another solution. In 2018, the Corps was awarded a new $112 million contract to create a fish passage complex. Mud Mountain's system differs from the traditional fish ladders; it's more like an airport terminal, with fish being directed to holding areas, identified, sorted, and then moved upstream in specially designed tanks.

As the largest trap and haul fish passage in the country, it was designed to move up to 1.2 million fish per year (and as many as 60,000 per day during peak pink salmon runs). The project was designed in collaboration with the Muckleshoot Indian Tribe, NOAA Fisheries, Cascade Water Alliance, and other regional partners, so that river management is a joint effort rather than just an engineering problem.

Fixing yesterday's solutions

A large proportion of the country's infrastructure has been constructed for nature control. Engineers are now re-engaging with those same projects to live in harmony with the ecosystem, rather than 'overpowering' them. Not everything is simple when you make choices. Fish passage facilities are expensive, must be monitored and adapted, and even sophisticated facilities can have unexpected problems, such as the loss of 43 fish in 2022 due to inadvertent Corps actions that led to reviews and corrective measures. Those incidents are also evidence of the evolution of conservation. The losses would probably not have garnered any attention decades ago. Today, they raise questions of public accountability and engineering changes.

A dam, then a retrofit

Mud Mountain Dam ultimately tells a larger American story. The country initially invested in protecting people, then later generations invested again to correct its environmental impacts, but not eliminating it; instead enhancing it. The new fish passage is no justification for the dam's having been constructed without a more ecologically conscious and holistic approach.

It's proof that public works can change in accordance with public values. The communities are still protected by the flood barrier as initially planned. Meanwhile, salmon are getting another opportunity to make a trip around their favourite United States. Sometimes it's not a choice between people or nature. It's about learning to be considerate of both.