Greybull Lagoon Wastewater Treatment Plant, Big Horn County, Wyoming

Greybull Lagoon is a municipal wastewater treatment facility located in Big Horn County, Wyoming, United States. The plant serves a small community of approximately 1,847 residents and operates as a lagoon-based secondary treatment system. Its location in the rural high plains of northern Wyoming places it within the Bighorn Basin, a semi-arid region where water resources are carefully managed. The plant provides secondary treatment, which is the standard level required under the U.S. Clean Water Act for municipal wastewater facilities. Secondary treatment typically involves biological processes that remove organic matter and suspended solids. The plant's designed capacity is 1,892.70 megaliters per year, and it currently discharges 832.79 megaliters annually, indicating it operates well below its design capacity. As a facility in the United States, it operates under a National Pollutant Discharge Elimination System (NPDES) permit issued by the Wyoming Department of Environmental Quality, which sets effluent limits to protect water quality. The treated effluent from Greybull Lagoon is discharged into a receiving water body within the Bighorn River watershed. The Bighorn River flows northward through Montana and eventually joins the Yellowstone River, a major tributary of the Missouri River. This downstream connection links the plant's discharge to the larger Mississippi River basin, ultimately reaching the Gulf of Mexico. The plant's operations are important for protecting local water quality in the arid Bighorn Basin, where streams and rivers support agriculture, wildlife, and recreation.

Greybull Lagoon discharges into a water body within the Bighorn River watershed. The Bighorn River flows north through Wyoming and Montana, joining the Yellowstone River, which is part of the Missouri-Mississippi river system draining to the Gulf of Mexico. The surrounding Bighorn Basin is a semi-arid region where water resources are critical for irrigation and ecosystem health. The plant's effluent contributes to base flow in local streams, supporting aquatic life and downstream uses. The area is home to species such as the Yellowstone cutthroat trout and supports migratory birds along the Pacific Flyway.