The high flow in the lower Waitaki River will continue for another 24 hours to bring greater benefits for the river.
Yesterday, Meridian Energy Ltd and Environment Canterbury (ECan) agreed to continue spilling a flushing flow down the river of between 920 and 940cumecs for the extra time.
Until late yesterday, no major damage had been reported to the river or its protections works, according to ECan.
Meridian external relations manager Claire Shaw said Meridian had the water available in its storage lakes of Pukaki and Tekapo.
With a prediction of more heavy rain tomorrow, it needed to keep a buffer to avoid a major flood in the lower river.
Meridian started increasing the level of the lower river from 6am on Monday, ramping it up to a flow of about 950cumecs by noon.
It planned to start lowering the river from noon yesterday.
ECan had started to see positive effects from the flushing flow, particularly at the mouth of the river where a new opening had been created through the coastal shingle bar.
Continuing the flow would also increase benefits of flushing didymo from the river, along with clearing vegetation from the fairway.
High flows above the average of about 380cumecs were expected to continue for some days, depending on inflows to the storage lakes, after the flushing flow was completed to maintain a buffer in Lakes Tekapo and Pukaki, ensuring Meridian's resource consents were not breached.
After low lake levels in August and September, heavy rain has filled the two storage lakes and Meridian has had to release water.
Yesterday, Lake Tekapo was at 709.704m above sea level, slightly lower than its maximum operating level of 710.9m.
Lake Pukaki at 532.372m was slightly above its maximum level of 532m.
ECan duty flood controller Tony Henderson said yesterday there had been no reports of major damage along the lower river and flood control works from the high flow.
"The biggest effect has been reopening the river mouth at the end of the mainstream," he said.
In advance of the flushing flow, ECan used a digger to open a breach in the coastal shingle bank so the river would flow straight out to sea, instead of going north to flow out a mouth about 3.5km north of where it usually was which had been created over the past three to five years.
