Flood-prone communities along the Ottawa River could be in for a nerve-racking weekend as waterways rise to levels last seen during the devastating floods of 2017.

The Ottawa River Regulation Planning Board (ORRPB) warned Thursday morning that days of rain coupled with warming temperatures would lead to river levels similar to those seen two springs ago when flood water deluged entire neighbourhoods, forcing hundreds from their homes.

Until now, the ORRPB said it expected levels to remain below that point.

Areas along the Ottawa River are under a rainfall warning this weekend, with up to 80 millimetres of rain possible in some areas from Thursday through Sunday.

All flood-prone areas along the Ottawa River from Lac Coulonge down to the Montreal Archipelago are at risk. - Ottawa River Regulation Planning Board

"Levels and flows on the Ottawa River from Lac Coulonge down to the Montreal region are expected to rise extremely rapidly starting this Friday due to forecast rainfall and snowmelt runoff," the board said in a news release.

"Major flood levels are expected to be exceeded over the weekend. Later on, flows and levels similar to those observed at the height of the May 2017 flood may be reached depending on the amount of precipitation received.

"All flood-prone areas along the Ottawa River from Lac Coulonge down to the Montreal Archipelago are at risk."

Gatineau Mayor Maxime Pedneaud-Jobin says residents should be ready for flooding this weekend. 0:51

Dams at capacity

The ORRPB said dams in the northern part of the river basin should be able to handle the increasing flow, but dams in the central and southern portions are already at capacity.

Residents are asked to contact their municipality if they believe their properties are at risk.

Communities including Gatineau, Ottawa and Clarence-Rockland, Ont., have started to distribute sandbags in flood-prone areas.

The warning from the ORRPB is the most widespread and significant warning of the several flood alerts from conservation authorities across the region.