Lake Stevens Restoration Efforts

[00:00:00]Lake Stevens, Snohomish County, Washington, is the county's largest lake in the heart of the city named for it, but it's struggling. By the 1980s, decades of phosphorus pollution had clouded the water and fueled algal blooms.

[00:00:11]Here's the issue with phosphorus in Lake Stevens. Decades of excess phosphorus has been settling to the bottom of the lake. Each summer, when oxygen runs low down there, the sediment releases it back into the water. It's a self-feeding loop that keeps fueling algae. This is called internal loading. The problem with internal loading is that the nutrients are in a loop, release, growth, death, decay, and back to release. This means that you will have poor water quality year after year, even if no nutrients are added. Cutting runoff alone can't break the cycle. The lake itself has to be treated. That's why the city of Lake Stevens, Snohomish County, launched an in-lake restoration program. In 1994, they installed a massive aeration system to keep oxygen high and phosphorus locked in the sediment. When that lost effectiveness, they switched approaches. Starting in 2013, crews began annual alum treatments, aluminum sulfate, which chemically binds phosphorus and seals it in the sediment for good. The results have been striking. Phosphorus dropped sharply, water clarity climbed from around 20 ft to more than 30, and the lake is now rated in excellent health.

[00:01:09]Aluminum sulfate has been used in lakes for over 60 years and has been found to be safe. The compound that remains is the same chemical found in antacids.

[00:01:16]Adding chemicals to lakes can be controversial, but in this instance, it is needed for the lake to be restored and to prevent harmful algal blooms, which can produce toxins harmful to humans and dogs. Want to learn more?

[00:01:27]Visit Snohomish County Lake Restoration page.