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 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.
Happily, we can report that water quality in Swan Lake is very good, with one exception. Despite excellent levels for nutrients, algae, sediments, and water temperature, the exception is that in some years dissolved oxygen (DO) sags to zero at the bottom of the south basin during the late summer and fall. Zero dissolved oxygen is a warning sign for lake water quality as anoxic conditions (zero oxygen) can lead to a release of the nutrient phosphorus from the bottom sediments which in extreme cases can rapidly turn a lake green with algal blooms. 2017 is the third year in a row that dissolved oxygen has hit zero (or very close to zero – it was 0.1% in 2015) in the south basin. This is the only time on record that Swan Lake has recorded no dissolved oxygen for three years in a row. Typically, the waters at the bottom are refreshed during years with high runoff, 2016/17 for example. Therefore, it’s puzzling why a DO sag should be occurring after a winter producing high runoff. Also of concern, is that in 2017 the waters at the bottom of the south basin nearly hit zero oxygen in August. Usually very low or zero oxygen is not measured until the fall; plus in October 2017, the bottom 2 meters (>6 feet) of the lake bottom had zero oxygen. We will continue our monitoring efforts in hopes of mapping the extent of the sag and determining its cause, in order to inform potential solutions.
The Final Water Quality Report for 2014 is available for download as a PDF here. This was the final report arising out of settlement ending the dispute with Kootenai Lodge Estates. It displays testing results from 2010-2013.