Mackay Sewage Lagoon - Custer County, Idaho Wastewater Treatment Plant

Mackay Sewage Lagoon is a wastewater treatment facility located in Custer County, Idaho, United States. It serves a small population of 517 residents, reflecting its role in a rural community. The plant provides secondary treatment, a standard level for small agglomerations under the US Clean Water Act. The plant's treatment process involves lagoon-based secondary treatment, which is common for small communities due to its cost-effectiveness and low energy requirements. With a designed capacity of 681.37 volume units and a current discharge volume of 567.81 volume units, the facility operates below its capacity, indicating room for growth or seasonal variability. The treated effluent is discharged into the local watershed, which ultimately drains into the Salmon River and then the Snake River system. This region is part of the Columbia River Basin, supporting diverse aquatic life and agricultural water uses. The plant's operation is regulated under the National Pollutant Discharge Elimination System (NPDES) permit program, ensuring compliance with water quality standards.

The plant discharges into the Salmon River watershed, a tributary of the Snake River, which flows into the Columbia River and eventually the Pacific Ocean. This watershed supports critical habitat for salmon and steelhead trout, species of ecological and economic importance. The secondary treatment provided by the plant helps reduce organic pollutants and protect downstream water quality in this sensitive river system.