Lake Hakuryû-ko is situated about thirty kilometers south-west of Yamagata City and occupies 7.13 ha in the northeastern part of Yonezawa Basin. From the geological point of view, this lake is considered to be the relic of the Paleo-Yonezawa Lake.
Even at the present time, in the surroundings the muddy marsh called “Ôyachi” spreads to an area of 900 ha.
The present study has been carried on with the aim at elucidating the limnological features with special reference to the ecology.
The annual deposition of suspended matter is estimated to be 70 mm in thickness. In other words, the lake has become shallower year by year. Under the circumstances, its maximum depth is now only 1.5 m. The bottom mud is composed of black organic matter under the reduced condition. The input of polluted water accelerates the rate of the eutrophication of this bog lake.
In the summer and the season of thaws, the development of thermal stratification is observed. The transparency of this lake is only 0.40.7 m. This value is rather small as compared with that of other lakes in the same latitude.
So far as the quality-of-water is concerned, this is characterized by the high concentration of chloride ion. At the littoral region, are found about 130 species of plants which contains 15 species of the alpine plants.
