Water Clarity Sampling & Monitoring


As part of the Whitefish Area Property Owners Association’s (WAPOA) water quality program, BPLA monitors and samples Big Pine Lake water on a monthly basis.  Good quality lake water is at the core of WAPOA’s efforts.  To know what water quality is, you have to take water samples and test the water.

Trophic State Indices (TSIs) are an attempt to provide a single quantitative index for the purpose of classifying and ranking lakes, most often from the standpoint of assessing water quality.  This is a measure of the trophic status of a body of water using several measures of water quality including: transparency or turbidity (using secchi disk depth recordings), chlorophyll-a concentrations (algal biomass), and total phosphorus levels (usually the nutrient in shortest supply for algal growth).

TSI ranges along a scale from 0-100 that is based upon relationships between secchi depth and surface water concentrations of algal chlorophyll, and total phosphorus for a set of North American lakes.  Its major assumptions are that suspended particulate material in the water controls secchi depth and that algal biomass is the major source of particulates.  The lowest value of zero would correspond to a secchi depth of 64 meters.  A value of 100 would correspond to a secchi of less than 3 inches – yuck!  A set of equations were then derived to describe these relationships with higher values corresponding to increased fertility, that is, more eutrophic.  An increase in TSI of 10 units corresponds to a halving of secchi depth and a doubling of phosphorus concentration.

In short, a higher TSI (unfavorable) means more algae in the water.  Water with high TSI levels may be unsuitable for swimming, clogged with plants, and supportive of rough fish.  For every one (1) point increase in the TSI, there is a 10 percent increase in algae in the water.

Big Pine Lake landowners and residents can help reduce TSI numbers:

Algae and other plants need phosphorus to grow.  So, keep phosphorus out of lake water by preventing run-off of driveway sediment and chemicals, by not using fertilizer with phosphorus, by maintaining septic systems, and by not mowing your lakeside lawn right up to the water’s edge.  Let the vegetation at water’s edge grow up to form a protective barrier.

Credit: A number of the features found on this page come from lakeaccess.org, http://www.lakeaccess.org/aboutus.html which is supported by the U.S. Environmental Protection Agency’s (EPA) Environmental Monitoring for Public Access and Community Tracking (EMPACT) program, as well as its sister project, Water on the Web, which is supported by the National Science Foundation