Oak Harbor STP - Wastewater Treatment Plant in Oak Harbor, Washington

Oak Harbor STP is a municipal wastewater treatment plant serving the city of Oak Harbor on Whidbey Island, Washington. The facility treats wastewater from a population of approximately 24,200 residents, making it a medium-sized plant in the region. Its location on an island in Puget Sound places it in a sensitive coastal environment. As a U.S. facility, the plant operates under the Clean Water Act and is subject to National Pollutant Discharge Elimination System (NPDES) permits issued by the Washington State Department of Ecology. For a plant of this scale, secondary treatment is typically required, and the permit sets effluent limits to protect receiving waters. The designed capacity is 1.00 million gallons per day, indicating the plant's treatment capacity. The plant's treated effluent ultimately reaches the Salish Sea, a critical marine ecosystem that supports salmon, orcas, and diverse marine life. The local watershed drains from Whidbey Island into Puget Sound, which is part of the larger Salish Sea basin. Protecting water quality in this area is essential for the health of the region's fisheries and coastal habitats.

The plant discharges into the Salish Sea via local streams and marine waters near Oak Harbor. This coastal environment supports a rich ecosystem including salmon runs, shellfish beds, and marine mammals. The watershed is part of the Puget Sound basin, which is ecologically sensitive due to its role in supporting endangered Southern Resident killer whales and commercial fisheries. Protecting water quality is critical for maintaining the health of these downstream habitats.