Lake Turnover and Stratification

In a recent post I talked about the various types of lakes based on their mixing classification. An understanding of the type of lake you are fishing on can give you a good indication of the depths where fish may be located at a particular time of year. In addition to preferred temperature for differing fish, the presence or absence of oxygen in the water plays a key role in where fish will move to. Fish will gravitate to areas that most closely satisfy both temperature and oxygen needs. The images below show a possible scenario for a moderately fertile, temperate zone, dimictic lake – a common type found in temperate areas such as Ontario. As mentioned in a previous post a dimitic lake will have turnovers in both spring and fall.

Fish will gravitate to areas that most closely satisfy both temperature and oxygen needs.

Lake turnover spring and summer

Dimictic Lake – Spring and Summer


Lake turnover fall and winter

Dimictic lake – Fall and Winter (red dots = dissolved oxygen)

A number of factors can change the situations above – both locally and lake-wide. For example:

  • Cooler temperature and oxygen rich areas such as at inflows of rivers and creeks
  • Power plants warm water discharge areas – warm zones
  • Underwater springs – cool spots in summer, can be magnets for fish during hot periods
  • In less fertile lakes oxygen levels will remain more constant allowing fish to remain deeper
  • In more fertile lakes oxygen loss will be a major factor, large algae blooms can severely diminish oxygen levels (dead zones within the lake)

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