Lake Monitoring Program

There are 27 lakes which have been identified as have high value, whether economical or environmental, and these lakes are monitored on a rotating basis.  PRWD collects water chemistry samples and lake profile data on the selected lakes to understand overall lake health and trends.  Samples are collected on a bi-weekly basis May through September. 

Field Data includes:

  • Temperature
  • pH
  • Dissolved Oxygen
  • Conductivity
  • Water Clarity (Secchi Depth)

Chemistry Data includes:

  • Total Phosphorus
  • Orthophosphate (Dissolved)
  • Chlorophyll-a

Lake assessments are done each year for lakes that are monitored and are included in the Annual Monitoring Report.

2017 Water Quality Monitoring Report

2018 Water Quality Monitoring Report

Specific Lake characteristics and summaries are in the link below.


Detroit Lake Curfman Lake Floyd Lake Little Floyd Lake
Lake Sallie Lake Melissa Long Lake Munson Lake
Johnson/Reeves Glawe Lake Fox Lake St. Clair Lake
Meadow Lake  Lind Lake    


Lake Level Monitoring

Lake level in recorded by a staff gage located throughout the District.  Gages are read on a bi-weekly basis.  Water levels for Detroit, Melissa, Sallie, and the Floyd Lake chain are updated bi-weekly on the tab to the right.

Monitoring Plan

Each year, the District prepares a plan that identifies the monitoring location and goals for the program.  The current monitoring plan can be viewed below.

2019 Water Quality Monitoring Plan

Lake Monitoring 2018

In 2018 the District spent $28,000 for seasonal labor, equipment and lab analysis to achieve the objectives of the monitoring program which include identifying water quality problem areas, quantify pollutant loadings, evaluate the effectiveness of BMPs, and promote understanding of District water resources and water quality.

The District studied the water quality of 12 District lakes (Floyds-Big, Little, North; Detroit-Big, Little; Curfman, Pearl, Sallie, Melissa, Abbey, Brandy, Lind, St. Clair, Long) during the monitoring season (April through October).

The District collects 8-10 water samples on a bi-weekly basis throughout the summer season on each lake.  Specific water quality data (total phosphorus,  chlorophyll-a, and Secchi disk depth) for each lake are compared to historical data collected in previous monitoring years.  Total phosphorus concentration readings represent the potential available phosphorus that will feed lake's aquatic plants and water column algae during the summer months.  These three water quality parameters are a measure of the water column's productivity.  Additional biological and physical parameters (i.e., macrophytes, dissolved oxygen, water temperature, PH, water levels, shoreline alterations/uses) and climatological information (air temperature, precipitation and notable climatic events) are also collected.  Phytoplankton was added this year for Big and Little Detroit, Sallie, and Melissa to collect additional information to study potential impacts on the on the aquatic food web due to Zebra mussel invasion.


The data is reviewed and used to characterize overall lake water quality and health, and examines trends over time to determine if each lake supports their designated uses for swimming, fishing, and/or aesthetics.  Lakes with increasing phosphorus trends and/or big swings in TP concentrations over time, are cause for concern.  An increasing phosphorus trend suggests something is changing in the lake, along the shoreline or in the watershed that is causing phosphorus concentrations to rise.  Caught early, intervention may stop or abate the source.  Lakes with big swings in phosphorus may be experiencing episodic phosphorus pollution.  Thsi information influences lake management decisions for continued protection and improvement of District Lakes.

Chart containing 2018 monitoring results, historical average, and lake standards for TP/Chl-a/Secchi depth

Floyd Lakes Zooplankton Project

This summer one of our interns, Connor Haugrud of Concordia College, is working on a research project investigating how the introduction of Zebra Mussel into the Floyd Lakes region has impacted the lake ecology and zooplankton populations. Zooplankton are microscopic animals that form the base of the food web that many other animals such as fish and waterfowl rely on for food. Since Zebra Mussels filter the water column heavily, the worry is that the zooplankton that are suspended in the water column will also be filtered and preyed on by the zebra mussels rather than young fish, taking down fish populations. Every four weeks samples are collected from the Floyd lakes as well as Long Lake to count zooplankton and look for any changes in populations since Big Floyd was found to be infected with Zebra Mussels in 2018. This research started in June of 2019 and will go until September.Populations will be compared to Long Lake, a non-infested lake, and water chemistry such as Total Phosphorus, Orthophosphate, Chlorophyll-a, Nitrogen, and Calcium will also be examined.

Pearl Lake Vegetation Survey - August 2018

 Pearl is a 261 acre lake with 60% (168 acres) classified as littoral zone (less than 15 ft depth).  Pearl has a maximum depth of 54 feet.  Therea re no MN DNR Aquatic Management areas on Pearl.


Survey Findgings:  Fifteen different types of plants were identified as well as one invasive species.  There is significant plant abundance throughout the littoral area as well as species diversity with over 60% of the sampling sites containing 3 or more plant types.  Seven submersed species make up the most common occurring plants (>10 occurrence) in Pearl Lake - Coontail, Flatstem pondweed, Bushy pondweed, Northern Milfoil, Sago pondweed, Large leaf pondweed, and Canada Waterweed.

187 survey points littoral area (less than 15 ft water depth)

  • 32 points had 5-6 plant species present
  • 100 points had 3-4 plants species present
  • 55 points had 1-2 plant species present
  • 0 points had no plant species present
  • 87 points had an invasive plant present - Curly Leaf Pondweed
18 survey points in deep water area (greater than 15 ft. water depth)
  • 1 point predominantly Coontail - 17 ft deep
  • 17 point had no plants found
14 Native Plant Species Present
  • 1 emergent (above water surface) plant species - Hardstem bulrush; 1 free floating species-Water moss; 1 floating leaf plant species-yellow waterlily.
  • 11 submergent (below water surface) plant species-Coontail, Flat stem pondweed, Bush pondweed, Northern watermilfoil, Sago pondweed, Large leaf pondweed, Illinois pondweed, Canada waterweed, Clasping-leaf pondweed, Whitestem pondweed.
  • 1 Invasive Plant Species - Curlyleaf pondweed.

Pearl Lake Survey.png

Munson Lake Vegetation Survey - August 2018

Munson is a 134 acre lake, with 48 acres (36%) of area classified as littoral (10%) are:  Northern watermilfoil, muskgrass, Illinois pondweed, Coontail, Sago pondweed, and yellow waterlily.  Of note, Burr-Reed, a native, emergent "look alike" plant to the invasive Flowering Rush species is found at the eastern and northern areas of Munson lake.  No invasive plant species were identified.  There are three Aquatic Management Areas (AMA), located on the west and southeaast sides which are fish spawning habitat.  This is the first comprehensive vegetation survey conducted on Munson Lake.

100 survey points littoral area (less than 15 ft water depath) at 50 meter intervals

  • 6 points had 7-9 plant species present
  • 34 points had 5-6 plant species present
  • 32 points had 3-4 plant species present
  • 12 points had 1-2 plant species present
  • 6 points had no plant species present (10-13 ft water depth)

12 Native Plant Species Identified

  • 3 emergent species (above water surface) - Burr-Reed, Hardstem Bulrush, Cattail
  • 1 floating leaf species - yellow waterlily
  • 8 submergent species (below water surface).  Northern water milfoil, musk grass, Illinois Pondweed, Coontail, Sago pondweed, Narrowleaf pondweed, Whitestem Pondweed

45 survey points in deep water area (greater than 15 ft water depth)

  • No plants foundMunson lake survey.png

Long Lake Vegetation Survey - August 2018

Long is a 409 acre lake with 152 acres (37%) classified as littoral zone (<15 ft depth), and has a maximum depth of 60 ft.  Long Lake has good water clarity.  The most common submersed species (>10%) are Muskgrass, Bladderwort, Sago pondweed, Northern Watermilfoil, Illinois pondweed, Yellow waterlily.  No invasive species were found.  This is the first comprehensive vegetation survey conducted on Long Lake.  The MN DNR maintains 3 aquatic management areas (AMA) consisting of dense bulrush beds located in the southwest, west and north areas which are fish spawning habitat.    Staff noted significant shoreline alteration (removal of aquatic vegetation, rip-rap installation, weed rollers) occurring next to these areas which may impact fish reproduction.

151 survey points littoral area (less than 15 ft water depth) @ 65 meter intervals

  • 3 points had 7-9 plant species present
  • 5 points had 5-6 plant species present
  • 64 points had 3-4 plant species present
  • 66 points had 1-2 plant species present
  • 3 points had no plants present (10-13 ft water depth)

21 Native Plant Species

    • 3 emergent species (above water surface).  Cattail, and Hardstem bulrush, Burr-Reed
    • 1 free floating species-Water Moss
    • 3 floating leaf species-Yellow waterlily, White waterlily, Floating-leaf pondweed
    • 14 submergent species (below water surface).  Northern water milfoil, Muskgrass, Illinois Pondweed, Coontail, Sago pondweed, Canada Waterweed, Flat-stem pondweed, Whitestem pondweed, Water Celery, Arum-leaved Arrowhead, Clasping-leaf pondweed, Slender Nitella


17 survey points in deep water area (greater than 20 ft water depth) @ 65 meter intervals
  • No plants found

Long Lake Survey.png

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Recent Water Levels
Detroit 1334.66 ft
Last Updated: 5/28/2019
Floyd(s) 1354.91 ft
Last Updated: 5/23/2019

Melissa 1329.05 ft
Last Updated: 5/28/2019
Sallie 1330.48 ft
Last Updated: 5/28/2019

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