A new system of hypolimnetic oxygenation called side stream pumping (SSP) is described. The SSP system uses liquid oxygen and a conventional water pump, whereas most other hypolimnetic oxygenation systems use compressed air and a special aeration chamber. The SSP system was tested in Ottoville Quarry, Ottoville, Ohio, during the summer of 1973. Hypolimnetic oxygen concentrations increased from less than 0.5 mg/1 to over 8.0 mg/1 during 2 months of operation, and thermal stratification was maintained. These improvements created a suitable habitat for cold‐water fish, but care must be exercised in the use of the SSP system to avoid potential problems with high, free carbon dioxide concentration
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