Lake Management Plan

go to PGOLID main pageChapter 1 includes an introduction and abstract
Chapter 2 includes the goals of PGOLID
Chapter 3 history covers geological formation to current district projects
Chapter 4 covers watershed characteristics of most of northwest Minnesota
Chapter 5 covers the main watershed around the Pelican Lakes
Chapter 6 covers the minor watersheds that surround Pelican Lake
Chapter 7 describes the types of data collected and why
Chapter 8 reports the data and water quality of inlets and outlets to Pelican Lake
Chapter 9 reports the water quality data for the Pelican Lakes

Chapter 10
Chapter 11 Safety and Buoys

 

Questions?
PGOLID Water Resource Coordinator
218-846-1465, email

Chapter 9: Lake Water Quality

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Fish Lake Trophic State Index

 

The resulting numbers from secchi depth, chlorophyll-a, and total phosphorus measurements cover different units and ranges and thus cannot be directly compared to each other or averaged. In order to standardize these three measurements to make them directly comparable, we convert them to a trophic state index using an equation. You can find the equations online at: http://dipin.kent.edu/tsi.htm.

The overall trophic state index (TSI) of a lake is the average of the TSI for phosphorus, the TSI for chlorophyll-a and the TSI for secchi depth; therefore, it can be thought of as the lake condition taking into account phosphorus, chlorophyll-a and secchi depth.

It is important to understand that Trophic States are defined divisions of a continuum in phosphorus and algal concentration. more information on trophic state index

Fish Lake water quality at site 201 has been monitored from 2003 to 2011. Site 202 has only been monitored in 2007-2008.

Results show that the overall average TSI for Fish Lake is 41. This TSI is the lowest (best) in the Pelican Group of Lakes. One reason is that it does not have any direct stream inlet discharging into it. Another reason is Pelican Lake is attached, therefore the phosphorus in that water is already diluted by the time it reaches Fish Lake. A third reason is Site 201, there is a 53 foot deep hole and the deeper the lake, usually the better the water quality.

For recreation, this lake is excellent. It also has a great sport fishery (walleye and northern pike).

Historical Results

In 2007-2008, both lake sites were monitored for water transparency, chlorophyll-a and total phosphorus. In 2011, just site 201 was monitored. From these measurements, the Trophic State Index was calculated. The results were similar. From these results, we can conclude that the water quality is fairly uniform across Fish Lake.

Table 1. 2011 TSI depth results.
Site Mean TSI Total Phosphorus TSI Chlorophyll-a TSI Secchi TSI
201 39.5 37.2 42.6 38.4
202 (2007-2008) 42 36 45 42

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