Eigthteen years have already passed since our first exploration of Lake Otori-ike. The difficult accessibility of the lake from the nearest village has made it ignored by the limnologists for these ten years. In August, 1973 the survey was carried out by the authors with the following results:
1) The lake has maintained the low productivity, i. e. it has been oligotrophic since 1955.
2) The ground water supply into the lake is 90, 000m³/day while the inflow of the surface water measures only 49, 000m³/day.