Water Quality Summary Report – 2012

Water Quality – 2012 Summary Report

The goal of the Swan Lake Water Quality Investigation is to collect water quality information for Swan Lake over a five year period (2010-2014) and compare to baseline data to develop trend analysis and to provide information to resource decision makers.

The project was initiated in 2010 by a contract between Kootenai Lodge Estates, Swan Lakers and the Whitefish Lake Institute. In 2011, the Swan Ecosystem Center expanded the scope of the project to include a late fall sample date and additional water chemistry analysis. Each year, Swan Lake is sampled four times. During each sample event, water quality parameters are collected from eight sites on the lake. At two of those sites, more in-depth water chemistry samples are collected for laboratory analysis.

Swan Lake is generally characterized by excellent water quality, with levels of nutrients, primary production, and chlorophyll (a) typical of an oligotrophic lake (low levels of nutrient inputs and low productivity). However, during late summer and early fall in the deepest parts of the lake, dissolved oxygen (DO) concentrations decline to low levels. This is particularly evident in the South Basin of the lake. Low benthic interface DO levels can increase mobility or release rates of phosphorus stored in the sediments via a reducing process given the right conditions. Provisional data from this project indicate stable to improving water quality trends in the lake for the Primary Targets investigated, however the cause and effect of the low DO concentrations in the South Basin need further analysis.

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