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The depth distribution of four fishes was studied using specially constructed vertical gill nets on Horsetooth Reservoir, Colorado (1960‐61). Of several environmental factors measured, water temperature was the one factor that exerted a measurable effect. Depth of capture increased for the rainbow trout, kokanee salmon, and white sucker as each summer progressed and in general followed the isotherms. The distribution of yellow perch was unaffected by temperature changes. Kokanee salmon were most abundant in waters of 51‐55° F. while the rainbow trout and white suckers were most numerous in 66‐70° F. waters.

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The water of the hypolimnion of West Lost Lake, a small Michigan trout lake, was pumped to the surface with a centrifugal pump and discharged into the epilimnion during a 10‐day period in midsummer. The volume of water displaced was 20.7 percent of the lake volume. As pumping progressed the thermocline lowered steadily and the thickness of the hypolimnion decreased. At the conclusion of pumping, the volume of the epilimnion had increased by 49.9 percent and the water of the hypolimnion had been displaced to the surface. The mean water temperature of the lake remained essentially constant during the experiment. In a 3‐week period following pumping, thermal conditions of the lake did not change appreciably. During pumping, conductivity and alkalinity increased in the epilimnion and in the bottom water, and the dissolved oxygen of the bottom water increased rapidly. The addition of bottom water increased the total phosphorus of the epilimnion by 2.8 micrograms per liter during the first 48 hours of pumping. Thereafter, phosphorus decreased to approximately the level encountered before pumping. An eight‐ to tenfold increase in the volume of phytoplankton of the epilimnion took place during the period of pumping. The volume of phytoplankton and the weight of seston remained high for a 3‐week period following the experiment.

No abstract