The flow into the Stanley Reservoir at Mettur dropped from 7,198 cubic feet per second (cusecs) on Friday to 3,324 cusecs on Sunday morning.
Public Works Department officials said the storage stood at 44.10 feet as against the full reservoir level of 120 feet. The storage was 14.298 thousand million cubic feet (tmc ft) against its capacity of 93.470 tmc ft. Water released for drinking purpose was 801 cusecs.
Poor rain in the catchments is the reason for the sudden drop in the flow, they added.
With the Tamil Nadu government ruling out water release for irrigation on the scheduled date of June 12 and the southwest monsoon not expected to bring in much rainfall, officials hope copious water will be released from Karnataka dams.