The Waitaki bridges on State Highway 82 in North Otago are not exepcted to reopen before the middle of next week due to heavy rain.
The Transport Agency closed the two single-lane bridges near Kurow on Tuesday because of flood damage to a pier.
It does not expect river levels to drop enough to carry out repairs until Monday.
Drivers are having to make lengthy detours. However, from Thursday, pedestrians and cyclists can use the bridges from 6am until 10pm.
The Canterbury Regional Council says floods in January also damaged river protection works on the Lower Waitaki and it is advising landowners to monitor the situation.
The swollen Waitaki River is forcing more water into already full Waitaki hydro lakes and into the Ohau, Pukaki and Tekapo riverbeds, it says.