Canterbury Regional Council is warning holiday makers along alpine rivers to watch out for rising river levels.
MetService has issued a severe warning for Fiordland, Westland and the headwaters of Otago and Canterbury, where it expects heavy rainfall for the next 24 hours.
South Canterbury duty flood controller Tony Henderson said although the weather may be fine further downstream, heavy rains in the mountains will quickly increase the volume of water in the rivers.
He told Summer Report that alpine rivers will be carrying more water than they normally would, and could rise quickly.
Mr Henderson said the warning also applies to hydro lakes in the Waitaki Valley.