Dissolved Oxygen Monitoring

The West Metro Area Fisheries office monitors dissolved oxygen (DO) levels in several lakes during winters. Testing is focused on publicly accessible waters that are: 1) marginal fish lakes with a history of fish die-offs/winterkill, 2) gamefish lakes with permitted, operable aeration systems, and 3) special fish-management situations.  Other groups, such as permitted aeration system operators, sometimes do their own testing.

Taking DO-level profiles allows us to assess aeration effectiveness and alerts us to potential winterkill conditions.  In most cases, we begin monitoring once ice is firmly established-- typically by mid-January. Our sampling usually stops when we see either oxygen levels stablizing near their lowest levels or winterkill indicators; other permittees/cooperators might continue taking readings.  Most sampled lakes are visited 1-3 times per winter.

We use a portable electronic meter to measure oxygen concentrations (unit of measure:  parts per million [ppm], equivalent to milligrams per liter [mg/l]).  Readings are taken from just below ice to the bottom (typically at 2-foot intervals).  Gamefish populations usually withstand DO levels above 2 ppm. 

Local Lakes Opened To Liberalized Fishing: NONE PRESENTLY.  Cynthia (Scott Co.) and Duck (Hennepin Co.) were opened from Feb 14-sunset Feb 23, 2014.  More information on liberalized fishing and list of opened lakes statewide can be found here.

Last updated:  March 14, 2014

Notes: Data are informational only and should not be considered complete or "official."  Winterkill might not occur despite low oxygen readings, or be limited in scope ("partial winterkill").  Fish die-off confirmation and detailed impacts on populations require observation and perhaps extra sampling.

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Carver County

Oxygen readings at surface/mid-depth/bottom; winterkill potential high when values are persistently below 2 ppm

Lake / Test Depth pre-Jan 5 Jan 5-15 Jan 16-26 Jan 27-Feb 6 2/7 - 3/14

Courthouse 55 ft

  11.4 8.6 6.1 aerated before ice-up 6.3 4.2 0.7

                    14 ft

  10.9 6.6 4.4  " " 8.4 1.8 1.3

Eagle*        12 ft

         0.7 0.5 0.5

Eagle*C      11 ft

11.8 7 3.2 6  5  1.5      1.9

Hydes        14 ft

         9.3 8.9 4.8

Lucy          16 ft

     18.3 2.4 7.5   4.6 2.5  2

Reitz          32 ft

        7  4.3 0.6

Susan*      15 ft

    15.2  10.2  8   2 1.4 0.7

Swede      6 ft  

         3.1 1.9 1.3

Virginia     26 ft  

         2.2 1.3  1

* lake with operating aerator      C cooperator/permittee data

 

Hennepin County

Oxygen readings at surface/mid-depth/bottom; winterkill potential high when values are persistently below 2 ppm

Lake / Test Depth pre-Jan 5 Jan 5-15 Jan 16-26 Jan 27-Feb 6 2/7-3/14

Duck            8 ft

   12.3 5.3 4.9      2.6 0.5 0.5

Half Moon C 25 ft

   6.2 2.8 0.4     2.6 0.5 0.2

Hyland* C    8 ft  

 12.3 9.5 2.6    10.5 7.6 4.2    

Mitchell*      6 ft  

     13.5 8.1 4.4    2.2 2.1 1.2

Mitchell*C    6 ft  

         3.1 2.8 2.8

Penn*          2 ft

    17.6   17    

Rebecca* C  23 ft

13  11.1  0.8 12.7 10.6 0.4      9  7.1 0.9

Red Rock*  16 ft

    14.5 8.2 7.2  1.1 1  0.5  

Red Rock*C 16 ft

         0.4 0.2 0.1

Snelling*     5 ft

    6.8 5.9 5.5    

Spurzem C  35 ft

  6.6 2.1 0.4      0.9 0.4 0.3

Starring      14 ft

         2.1 1.6 1.2

* lake with operating aerator      C cooperator/permittee data

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Scott County

Oxygen readings at surface/mid-depth/bottom; winterkill potential high when values are persistently below 2 ppm

Lake / Test Depth pre-Jan 5 Jan 5-15 Jan 16-26 Jan 27-Feb 6 2/7-3/14

Cedar*         10 ft

  16.1 12.7 11.8      8.5 8.3 4.5

Cleary* C       7 ft

10.8 3  1.8   4.7 3.5 0.9    

Cynthia          6 ft

  8.4  7  7     0.9 0.8 0.8

McColl*         8 ft

       4.8 2.2 2.0  

McMahon*    16 ft

  13.5 8.1 5.5     4.9 2.5 1.8

Murphy* C  18 ft   

8.5 3.9 1.6    4.6 0.9 0.3    

O'Dowd*    22 ft

  8.3 6  4.1     4  3.8  2

Schneider     9 ft

   3.3 2.6 2.4      

St Catherine  5 ft

  4.6 3.4 3.5      

Thole*        12 ft

  7.3 5.6 4.5     3.8 3.3 1.9

* lake with operating aerator     C cooperator/permittee data

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