The Big Fork River Watershed is in the U.S. portion of the basin only and is 2,073 square miles in size.  Development pressure is moderate in most areas, with occasional farms being parceled out for development, recreation or country homes.  Intensive watershed monitoring began in the Big Fork River watershed in 2010 – the monitoring was comprehensive and included the collection of samples from lakes, streams and groundwater. Biological data were collected from rivers and streams to assess aquatic life and aquatic consumption. Water chemistry information was collected to assess surface waters for aquatic life and aquatic recreation as well as computing pollutant loads through the state’s Major Watershed Load Monitoring Program (MWLMP).

The assessment results for the Big Fork River Watershed indicate that the condition of the lakes and streams are good to very good, even though there were a few impairments found. The most widespread impairment found in both lakes and rivers is due to high mercury levels, limiting the human consumption of fish. The remaining impairments throughout the watershed consisted of low dissolved oxygen (DO), fish and macroinvertebrate and nutrient impairments. Many of the aquatic life impairments are the result of natural conditions within the watershed. For more detailed information on the monitoring and assessment that was done, please access the full report at In October 2017, the strategy report was complete, recommending areas where restoration and protection are needed – the report is available at the link above; as well, information on this watershed can be found at