The release, originally planned for 24 hours, swelled the river from 6am on Monday, reaching its maximum at midday Monday.
On Tuesday, it was supposed to fall from midday but, after consultation with Environment Canterbury (ECan), it was decided to keep it going for a further 24 hours to maximise the benefits to the river.
Those include flushing the river of didymo, and consolidating a new river mouth at the end of the main stream, instead of about 3.5km further north, where it had shifted over the past three years.
The release was to ease pressure on storage in Lakes Pukaki and Tekapo, which were over-full.
Meridian needs to maintain a buffer in the two lakes so it can cope with any heavy rain in the catchment.
Meridian's external relations manager Claire Shaw said yesterday the river started falling from midday and at about 5pm was at 750cumecs.
It has to be lowered according to conditions in Meridian's resource consents to operate the Waitaki hydro generation system.
Today, the flow was expected to reach 450 to 500cumecs, where it could be held for a few days.
However, that would depend on in-flows into the storage lakes, and the extent of a heavy rain warning for southwest New Zealand until Sunday.
