Cell counts of E. coli in the water of Lake Nakanoumi were enumerated monthly by Eijkman method from 1966 to 1982. The results obtained at one point of Lake Shinji and 4 points of Lake Nakanoumi in 1981 when the most abundant population was observed among the research period were also shown.
1) The counts in the water of Lake Nakanoumi were rather few and showed little variance through the 5 years.
2) The cells increased in summer, while in winter they decreased and, frequently, were not detected.