Suizenjirori (Aphanothece sacrum (Sur.) Okada) is a one of freshwater unicellular Cyanobacterium. However, there is little academic paper with regard to Aphanothece sacrum (Sur.) Okada, because of the difficulty getting it as experimental material. The purpose of this paper is to describe the groundwater environment for the conservation of Aphanothece sacrum (Sur.) Okada. Recently, spontaneous Suizenjinori has faced to the crisis of extinction by decrease of water flow and water pollution with the city development. The resistivity image profiling obtained from electric prospecting, stratum division picture with ground information database, water quantity and water examination were investigated to get the foundations data for Suizenjinori conservation. The spring rate of Lake Ezu area was ca. 400, 000m³/d and decreased about 10% of the water flow during the experimental period (from 1992 to 1999). There are groundwater come out from three aquifers i. e. most upper aquifer and Togawa lava upper and lower sediment layers in Lake Ezu. It is considered to mix the groundwater of Togawa lava layer and its upper sediment layer in the neighborhood of Lake Ezu. It is marked by a lower concentration of aluminum in Suizenjinori pond than the other spring pond. It is regarded to influence the basement water under Togawa lava to inhabit Suizenjinori.