In connection with these lakes, the writer studied in the water temperatures together with the air temperatures on three occasions, namely, in the middle of Aug. 1933, in the begining of July 1934, and on the last of July 1934 being assisted by Messrs. K. KOBA, N. OBARA, I. NAGATU, N. ANDÔ, and K. SIBATA.
Accurate observations of deep water temperature were attempted by means of a RICHTER & WIESE reversing thermometer attached to an EKMAN water bottle. The data obtained are given in Table. 5 (pp. 351-355).
The effects of climate and lake morphology on the thermal conditions of these lakes appear to be alike in all of them. Since all these lakes, being situated in hollows are well protected from wind, the differences in thermal conditions in summer are due not to winds, but to another cause, namely the inflowing of cold spring and cold river water which, except in the case of Subalpine lakes, which are fed by turbid water of large rivers formed by melting snow, however do not as a rule play so great a rôle in Japanese lakes.
We can easily classify them into three thermal types.
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The above figures are those for the last ten days of July, 1934.
The Ôike Type corresponds to the thermal type of L. Hangetuko, the Otikutinoike type to the Oodairanuma subtype, and the Aoike type to the Tutanuma subtype of the writer, according to his published paper on thermal types of Japanese lakes in summer.⁽¹⁾
The Ôike type includes small and deep lakes with or without warm inflowing water that does not disturb the deep water temperature. The water of the bottom is very cold. A temperature as low as 3.88°C was observed at 25 meters in Ôike lake in July 1934. The Otikutinoike type includes on the other hand, those in which enter a large amount of cold water from the springs in the upper stream. The Aoike type corresponds to the thermal conditions of small spring ponds.
Slight dichothermics were discovered in Lakes Aoike and Ôike in the Kosigutinoike Lake Group. That in the former is due to the inflowing of two kinds of springs with different temperatures and salinities at different levels. Although the latter is probably due to sublacustrine springs, it is probable that its warm bottom temperature is a sign of the autumnal warming of the previous year, a possibility recently proposed by FINDENEGG in the case of Austrian lakes.
The water of spring ponds were blue and very transparent. A 25cm white disc was visible down to their bottoms (7 to 9 meters). Lakes withh poor phytoplankton production were green, and their transparency exceeded 5 meters. The maximum value in the summer was 8.3 meters. The transparency of lakes with abundant growth of Diatomn, chiefly Astrionella formos and Melosira granulata, were reduced to 2-3 meters. The most turbid water (transparency between 0.7 to 1.6 meters) was in Lakes Itobatakenoike and Gobônoike, due to thick water bloom of the blue algae Anabaena sp. Suspension of fine clay particles derived from the pearlitic tuff that composes the region also helped to reduce the transparency of all lakes of the Tugaru Zyûniko Lake Group.

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