The consequences of underworking Lake Kalina situated in the area of the Viru main field of the Estonian oil shale deposit are given. The mining has been carried out by room-and-pillar method. Both the preliminary stage and the period of payable seam extraction under the rake at the depth of 49.5 m from the earth surface were accompanied by a large complex of exploration and research works. The respective water level lowerings in the aquifers of the roof were recorded The level of the lake water has undergone no essential changes, and the lake proceeds under the hanging regime. It is expected to carry out an artificial roof caving under the lake to avoid uncertainties after the exploitation.