Three lakes, among the Zy ?? niko lake group in Aomori Prefecture, Japan, have been studied in relation to their limnological conditions. Observations showed that at the beginning of the summer, the hypolimnions of Lake Koikuti and Lake Oike show marked poildlo or dichotomous stratification of temperature. The present study proved these stratifications to be due to the effect of underground feeding. Such stratifications are, however, subjected to change into the direct stratification by August. The dissolved oxyg ?? n in the hypolimnion of these lakes shows distinct stratification from as early as mid May, thus exhibiting marked anerobic condition from this afterwards. In Lake Otikuti, the depth of which is about 21 meters, the anerobic layer measures 10 meters in thickness.