Water Quality-Trophic State Index

Trophic Index

Carlson’s Trophic State Index (TSI) is used by professionals and lay lake advocates to describe how productive, or trophic, a lake is.

TSI is based on three different measures of lake productivity: water transparency as measured by the Secchi disk (SD), Chlorophyll ‘a” (Chl ‘a’), and total phosphorus (TP). Mathematical equations for each of the three parameters are calculated to transform numeric values into an index ranging from one to 100. Data is collected during the growing season, May to September. May data sets a base for the year, but only June to September data is used in the TSI assessment.

Lake Shamineau’s volunteer Water Quality Committee (AL & Bob) collect water samples monthly and send them to RMB Environmental Laboratory for analysis.

Test data for Lake Shamineau can be viewed at the MNDNR website by clicking here:  

The Secchi disk value is an indirect measure of algae blooms. A black and white disk is lowered and raised to determine the depth of water clarity measured by the length of line connected to the disk.

Chlorophyll ‘a’ is a pigment found in algae and is a direct measure of algal quantity (biomass).

Total phosphorus is relatively stable throughout the year and is usually a major factor in limiting algae growth.

Carlson’s Trophic State Index

< 30  Oligotrophic; clear water; high DO throughout the year in the entire hypolimnion
30-40  Oligotrophic; clear water; possible periods of limited hypolimnetic anoxia (DO =0)
40-50 Moderately clear water; increasing chance of hypolimnetic anoxia in summer; fully supportive of all swimmable/aesthetic uses
50-60 Mildly eutrophic; decreased transparency; anoxic hypolimnion; macrophyte problems; warm-water fisheries only; supportive of all swimmable/aesthetic uses but “threatened”
60-70 Blue-green algae dominance; scums possible; extensive macrophyte problems
70-80  Heavy algal blooms possible throughout summer; dense macrophyte beds; hypereutrophic
> 80 Algal scums; summer fish kills; few macrophytes due to algal shading; rough fish dominance


TSI Graphic Representation

A.W. Research Laboratories TSI Mapping

In August 2012,  the Lake Shamineau Association hired A.W. Research Laboratories Inc. of Brainerd, MN to do an aerial mapping survey of the lake. Owner Alan Cibuzar presented information at our Fall 2012 Membership Meeting. A copy of the report can be viewed HERE.