While rising water levels due to melting snow and ice is common in the spring, cool weather and large spring snowstorms added to the issue. The March 2017 North American blizzard added another 70 centimeters of snow along the Saint Lawrence River Valley. This issue was exacerbated by heavy rain in April and early May 2017. Montreal alone received 156 millimeters of rain in April, twice the monthly average and nearly beating the record of 159 mm from 2005.
On 30 April, the level of the Saint-Maurice River began to rise, causing concern among the public. The rising floodwaters washed out portions of Quebec Route 155 and the road between La Tuque and the Atikamekw community of Wemotaci. Route 155 remained closed to traffic until 8 May, when it was reopened to all but heavy vehicles. Until this point, people traveling between La Tuque and Trois-Rivieres needed to drive through the Saugenay Region, then down to Quebec City and Autoroute 40, which tripled the amount of travel time.
Outaouais
Flooding began in the Outaouais region on 20 April, when the Ottawa River flooded areas of Pontiac, while the Petite-Nation River flooded roads in the town of Saint-André-Avellin. Surrounding towns of Ripon, Cayamant, Duhamel, Gracefield, Montpellier and Waltham also experienced flooding, isolating some residents. Portions of Quebec Autoroute 50 were flooded on 7 May after nearly two feet of rain over the proceeding two days. Emergency work by Transports Quebec reopened two lanes of the three-lane highway by 9 May. The closure of Autoroute 50 and surrounding flooding caused both the federal government and provincial government to close their offices in Gatineau, rather than have employees risk coming in. Transport Quebec closed several roads on 7 May, including the Galipeault Bridge, due to rising water levels. The Ottawa River crested on 8 May for most citizens in the Ottawa River Valley, specifically between Mattawa and Hawkesbury, Ontario. In Gatineau, the river reached a level of 45.08 meters, down 10 centimeters from previous reports. The local fire department in Gatineau rescued and evacuated approximately 533 people, with the Red Cross providing shelter for close to 1000. In Ottawa, Mayor Jim Watson said that 346 residences had been flooded in the city, with 90% of them found in West Carleton-March Ward. As of 10 May, the Canadian military had stationed 2,200 troops in Quebec, as well as dozens of military boats, helicopters, armoured vehicles and engineering equipment, and a naval frigate,.
Montérégie
Towns between Montreal and Ottawa, faced flooding near the end of April. This area is where the Ottawa River and the St. Lawrence River meet, and includes Lac Saint-Louis, Lac Saint-François and Lac des Deux-Montagnes. The town of Rigaud declared a state of emergency on 20 April to deal with rising floodwaters, calling for the evacuation of 470 households.
