The water level has not reached the maximum level at least for the past six years due to shortage of rainfall, but raining was good since July causing the water level to cross the 3215 feet mark, an MeECL official said.
The highest level at Umiam, mostly fed by rivers originating from East Khasi Hills, was 3,207 feet last year.
"It will be necessary to release the water of Umiam Dam in case of heavy rainfall as the water has crossed the 3215 mark by 0.64 feet at 4 PM today, MeECL Director (Generation) E Lyngdoh told PTI.
At present, the two power producing units - Umiam and Leshka Hydel Projects - are producing about 200 MW of power.
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The dam had earlier this year hit local headlines for its very poor power generation causing the state to undergo long hours of power cut for months.
The water has to be released for safety of the dam but it would be done in a phased manner to prevent inundation of of areas in the downstream, Lyngdoh said.