River Rock County W and S District Wastewater Treatment Plant, Gallatin County, Montana

River Rock County W and S District is a municipal wastewater treatment plant located in Gallatin County, Montana, United States. The facility serves a population of approximately 3,100 residents in the River Rock area, operating as part of the county's water and sanitation district infrastructure. The plant provides secondary treatment, a standard level for small communities in the United States under the Clean Water Act. With a designed capacity of 757.08 units and an average daily discharge of 643.52 units, the facility operates below its capacity, indicating room for future growth. US plants of this scale typically require National Pollutant Discharge Elimination System (NPDES) permits issued by the Montana Department of Environmental Quality. The treated effluent is discharged into local waterways within the Missouri River basin, which ultimately drains to the Mississippi River and the Gulf of Mexico. The plant plays a key role in protecting water quality in the Gallatin County area, supporting downstream aquatic ecosystems and recreational uses.

The plant discharges into the Missouri River watershed, which flows through Montana and joins the Mississippi River before reaching the Gulf of Mexico. This region supports diverse aquatic life, including native fish species, and the treatment plant helps maintain water quality for downstream communities and ecosystems. The area's cold-water streams are sensitive to nutrient pollution, making secondary treatment important for ecological health.