Meridian Energy is about to get rid of excess water from the southern hydro lakes.
Heavy rain has filled the lakes to capacity and the spillage is seen as vital.
Lake levels were at a record low last winter, prompting a campaign to encourage electricity conservation.
Canterbury Regional Council is warning people who may be camping and fishing along the Waitaki River on Monday to watch out for a sudden rise in water levels.
It says water levels are likely to be higher for about 24 hours.
While the river has the capacity to handle the extra flow, the council says people should still be careful.