Lake Aviemore will fluctuate by almost 3m in July during tests by its owner, Meridian Energy, as part of an upgrade of the power station's control system.
The tests were due to start on Monday, but have now been postponed to July, on dates yet to be set, because heavy rain along the Southern Alps is raising the level of storage lakes.
Environment strategy manager Jeff Page said the testing was required to get accurate data for a new programmable logic controller, a digital computer that controls the generating units.
The testing would cover the full operating range of Lake Aviemore, from 267.7m above sea level to 268.3m, one test dropping 2.65m from its maximum level.
Lake Waitaki may also be affected.
This testing is required to cover the full operating range of the power station's head and tail water levels.
Mr Page said the changing lake levels posed no operational or public safety issues, although the lower sections of some Aviemore boat ramps may become exposed for one day, which could affect boat owners wanting to launch.
However, the low lake level also gave the chance for repairs to ramps.
