Cowlitz Water Pollution Control Plant | Longview, Washington Wastewater Treatment

The Cowlitz Water Pollution Control Plant is a municipal wastewater treatment facility located on Fibre Way in Longview, Washington, within Cowlitz County. It serves an estimated population of 39,877, placing it in the medium-agglomeration category under U.S. regulatory frameworks. As a U.S. facility, the plant is subject to the Clean Water Act and operates under a National Pollutant Discharge Elimination System (NPDES) permit issued by the Washington State Department of Ecology. For a plant of this scale, secondary treatment is typically required, with additional nutrient controls if discharging to sensitive waters. The plant's treated effluent is discharged into the Cowlitz River, a major tributary of the Columbia River. The Columbia River system supports diverse aquatic life, including salmon runs, and ultimately drains into the Pacific Ocean. The plant plays a key role in protecting water quality in this ecologically significant watershed.

The plant discharges into the Cowlitz River, which flows into the Columbia River approximately 30 miles downstream. The Columbia River is the largest river in the Pacific Northwest, supporting critical salmon and steelhead populations. The lower Columbia River estuary provides important habitat for migratory birds and marine species. The plant's operations help maintain water quality in this dynamic river system, which is subject to tidal influences near the coast.