Since 2015, Swan Lakers’ volunteers have been conducting Swan Lake water quality monitoring efforts 4 times a year: ice off (March/April), runoff (June), mid-summer (August), and late fall (October). Water quality information is gathered at one-meter intervals from top to bottom with a multi-meter instrument that the Flathead Lake Biological Station allows us to use. Also, water samples are drawn from different depths (5m, 30m, and 0-30m integrated) and sent to the Bio Station for chemical analysis in their laboratory. The monitoring occurs at the deepest points of the north and south basins of Swan Lake. Each of these is approximately 120 feet deep.
The following charts display the results of Swan Lakers’ water quality monitoring efforts. The first chart describes the plan for protecting Swan Lake’s water quality, as adopted by the Montana Department of Environmental Quality. Those that follow display water clarity findings, dissolved oxygen concentrations, as well as phosphorus, nitrogen, and chlorophyll concentrations. You will note that dissolved oxygen dropped to zero in the south basin in the fall of 2015 – 2017. Happily, it rebounded to higher levels in 2018 – 2021.
The gathering of this data is critical to identifying long-term trends in water quality and identifying threats. The State of Montana does not regularly monitor the water quality of Swan Lake. Most of the monitoring and water quality data for Swan Lake over the last 20+ years have come from the Swan Lakers, the Bio Station, Whitefish Lake Institute, and associated volunteer efforts. The findings compiled by the Swan Lakers are the only active time series of data for tracking the water quality of our lake.
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