Parshall Lagoon Wastewater Treatment Plant, Mountrail County, North Dakota

Parshall Lagoon is a municipal wastewater treatment facility located in Mountrail County, North Dakota, United States. The plant serves a small population of approximately 903 residents and is situated in a rural area of the state. As a lagoon-based system, it provides secondary treatment to meet federal and state water quality standards. The plant has a designed capacity of 681.37 cubic meters per day and currently discharges an average volume of 264.98 cubic meters per day. Under the US Clean Water Act, facilities of this scale are typically regulated through the National Pollutant Discharge Elimination System (NPDES) permit program, administered by the North Dakota Department of Environmental Quality. Secondary treatment is the minimum standard required for municipal wastewater plants in the United States. The treated effluent from Parshall Lagoon ultimately drains into the Missouri River watershed, which flows into the Mississippi River and then to the Gulf of Mexico. The plant's location within 10 km of the coast is notable, though North Dakota is landlocked; this likely refers to proximity to a major river or lake. The receiving water body supports aquatic life and is part of a larger drainage system that affects downstream ecosystems.

The plant discharges into the Missouri River basin, which flows into the Mississippi River and eventually the Gulf of Mexico. This watershed supports diverse aquatic species and is an important migratory corridor for birds. The region's semi-arid climate and agricultural land use mean that maintaining water quality in the receiving waters is critical for both ecological health and downstream human uses.