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. Others, such as permitted aeration system operators, sometimes do their own oxygen 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. More information on liberalized fishing and list of opened lakes statewide can be found here.

Last updated:  February 14, 2018

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 most values drop and remain below 2 ppm

Lake / Test DepthJan 13-31Feb 1-15Feb 16-28March 1-31

Courthouse       14 ft

 13.7   9.3   7.7   

                            50 ft

13.2   10.6    2.0   

 Susan*  C          16 ft         

 14.6    9.1    0.8 10.6    4.9    1.1  


    

 

    

 

    

* lake with operating aerator      C cooperator/permittee data

 

Hennepin County

Oxygen readings at surface/mid-depth/bottom; winterkill potential high when values drop and remain below 2 ppm

Lake / Test DepthJan 15-31Feb 1-15Feb 16-28Mar 1-31


    

 

    

 

    

 

    

* 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 drop and remain below 2 ppm

Lake / Test DepthJan 9-31Feb 1-15Feb 16-28Mar 1-31

Quarry          40 ft

13.0    12.4    9.3   
 O'Dowd       22 ft  15.0    11.7    5.7  
     
     
     

* lake with operating aerator     C cooperator/permittee data

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