At the same time, to take advantage of the low flow, a digger is clearing gravel from below the Waitaki dam.
Yesterday, the Waitaki's flow dropped quickly from about 240cumecs mid-morning to about 185cumecs yesterday afternoon.
It was expected to reach 130cumecs between noon and 5pm today.
Meridian spokesman Alan Seay said the low flow was because Meridian had switched generation to Manapouri to save water in the Waitaki system.
Manapouri had reached close to its minimum operating range and, during the past month, Meridian had been generating out of the Waitaki system, letting flows in the river reach 400cumecs.
Last weekend, rain in the Manapouri-Te Anau area boosted operating levels for Manapouri, making generation available there.
In the past week, the Waitaki has flowed between 250cumecs and 300cumecs, a measure of the reduced generation.
Yesterday, rain was falling along the southern divide, and the MetService issued a heavy-rain warning of up to 100mm from 8am yesterday to 6pm today.
By mid-afternoon, Mt Cook had received 51mm of rain.
The annual Waitaki River jet-boat race, being run by Jet Boating Otago today, will still take place, although organiser Pete Templeton said the low flow would mean more challenging boating.
The launch of boats might be transferred to the north bank, he said.
