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 stabilizing 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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Hennepin County Scott County
Carver County
Oxygen readings at surface/mid-depth/bottom; winterkill potential high when most values drop and remain below 2 ppm
| Lake / Test Depth
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Jan 13-31
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Feb 1-15
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Feb 16-28
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March 1-31
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Courthouse 14 ft
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13.7 9.3 7.7
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50 ft
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13.2 10.6 2.0
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Susan* C 16 ft
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14.6 9.1 0.8
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10.6 4.9 1.1
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* 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 Depth
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Jan 15-31
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Feb 1-15
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Feb 16-28
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Mar 1-31
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* lake with operating aerator
C cooperator/permittee data
Scott County
Oxygen readings at surface/mid-depth/bottom; winterkill potential high when values drop and remain below 2 ppm
| Lake / Test Depth
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Jan 9-31
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Feb 1-15
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Feb 16-28
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Mar 1-31
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Quarry 40 ft
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13.0 12.4 9.3
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| O'Dowd 22 ft
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15.0 11.7 5.7
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* lake with operating aerator
C cooperator/permittee data
