The hydroelectricity lake watchdogs are a statutory appointed body and spokesman Grant Fyfe said the lake was approaching the minimum permitted level of 338m above sea level (asl).
A reading from the Otago Regional Council water flow website at 4pm yesterday recorded a level of 339.24m asl for Lake Hawea.
Mr Fyfe said despite weekend rain, the guardians were concerned about the amount of water being released downstream by electricity generator Contact Energy.
"We don't want to see the lake getting down to emergency levels," he said.
He estimated the lake held enough "draw-down" water to last about 11 days and called for Contact to conserve the lake's existing water level.
The level of Lake Hawea is controlled by Contact, which uses the lake to store water for the downstream Clutha power stations at Clyde and Roxburgh.
Contact Energy spokesman Jonathan Hill said recent rain made a small impact on Lake Hawea and similar weather patterns were likely to deliver more over the coming weeks.
The company was aware the lake was approaching the emergency minimum level, but there were a lot of variables in terms of "when, or if, that level might be reached", Mr Hill said.
A 2007 resource consent condition allowed Contact to access 2m of additional storage - between 338m and 336m - during certain conditions, in the national interest, when the electricity system required reserve capacity, Mr Hill said.
