Whitefish Area Property Owners Association





The maps, made at the beginning of 2010, show the latest data through the end of the 2009 testing season. 

Volunteers sample more than 30 lakes every month from May through September.   They have done this for many years. 

A Secchi disk is used to measure the visibility of the water, and water samples are analyzed for chlorophyll-a and phosphorus.

The three readings are combined to give a Trophic State Index score.

This is often abbreviated as the TSI score.

A lower score is better.  The lowest we see are TSI's in the 37-40 range.

This is clear water with excellent visibility, excellent water for game fish and swimming.

Every rise of one TSI unit indicates an increase of 10% in the amount of algae present.

So a lake with a TSI of 44 has 40% more algae than a lake with a TSI of 40.

There are area lakes with TSIs as high as 54.  Their water transparency is much less, they have more algae, and rough fish are found.







 
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