Marysville Lagoon Wastewater Treatment Plant, Marysville, Washington

Marysville Lagoon is a municipal wastewater treatment facility serving the city of Marysville in Snohomish County, Washington. With a population served of around 60,660, it is classified as a medium-to-large agglomeration under US regulatory standards. The plant's designed capacity is 1.00 million gallons per day, and it operates under the US Clean Water Act, which requires NPDES permits for all discharges to surface waters. For facilities of this scale, secondary treatment is typically mandated, with additional nutrient removal if discharging to sensitive water bodies. The treated effluent from Marysville Lagoon ultimately drains into the Snohomish River basin, which flows into Puget Sound. This estuarine environment supports diverse aquatic life, including salmon runs and marine species, making proper treatment essential for ecosystem health.

The plant's discharge enters the Snohomish River watershed, which flows into Puget Sound, a large estuarine system in the Pacific Northwest. Puget Sound supports critical habitats for salmon, orcas, and other marine life. The region's high rainfall and seasonal flows influence dilution and transport of treated wastewater, requiring careful management to protect water quality and aquatic ecosystems.