The surrounding area of the Nabekoshi Pass in Yamagata Prefecture is famous for a heavy snow fall in winter. The district is characterized by an abundance of small lakes and swamps, among which Lake Wakahata-numa is a representative one. In this paper, this lake is treated from the standpoint of regional limnology. The results of the investigations are summarized in the followings :
1. The morphometrical data calculated from the bathymetric map are :
Surface area…1.42×104m2
Length of shore line…508m
Maximum depth…11m
Volume…6.48×104m3
Shore development…1.2
The amount of seepage from the bottom of the lake is about 1, 400m3 per day. In the season of rapid thaws, the lake water is turned over by the inflowing melt water only for four days.
2. In mid-summer, the development of thermal and chemical stratifications is observed in this lake.
3. The main constituent of dissolved minerals is sodium chloride derived from the atmospheric salt which is transported by the melt water.
4. Total amount of dissolved substances in this lake is estimated at about four tons from summer to autumn. At the season of thaws, it decreases to about a half.
