A flush of the Waitaki River has been extended after Meridian Energy was granted permission to continue flooding of the river for another 24 hours.
Meridian Energy began releasing greater than normal volumes of water down the River on Monday morning and was to have finished at midday on Tuesday.
The company has now been granted permission by the Canterbury Regional Council to extend the flush for another 24 hours, to midday on Wednesday.
Duty flood controller Tony Henderson says the flush is being monitored and the water levels have been contained, with no damage to the environment.
Benmore dam has been at capacity after weeks of heavy rain.
Hydro lakes were at record low levels last winter, causing a campaign to be held to encourage conservation of electricity.