Forecast for 2026-04-20

Spring runoff from the unregulated portion of the basin is currently at its highest, with northern reservoirs retaining a large portion of the spring runoff to reduce flooding in the downstream river system. Water levels and flows are expected to continue increasing from Mattawa to Pembroke over the next few days and are expected to start stabilizing today between Lake Coulonge and Lake Deschenes, and Wednesday between Gatineau-Hull and Carillon. Minor flood levels in Mattawa could be exceeded over the next few days, and have been exceeded from Pembroke down to Carillon. Major flood levels have been exceeded in flood prone areas from Lake Coulonge to Lake Deschenes, and are expected to be reached or exceeded today from Gatineau-Hull to Carillon. The minor and major flood levels are defined on the Home page in the Special Feature section. Downstream of Pembroke, water levels are expected to slowly increase until a peak is reached on Tuesday or Wednesday. Our website Forecasts section provides expected water levels over a four-day horizon in several areas. On April 20 peak level estimates are close to 2023 peak levels, as follows: Pembroke (113.20 m), Lake Coulonge (108.75 m), Chats Lake (75.85 m), Lake Deschenes (60.30 m), Gatineau -Hull marina (44.70 m) and Thurso (43.10 m). These are lower than the 2023 peak levels by 10 cm (Pembroke), 0 cm (Lake Coulonge), 5 cm (Chats Lake), 5 cm (Lake Deschenes/Britannia), 0 cm (Gatineau -Hull marina) and 10 cm (Thurso). Over the next two weeks, levels from Lake Coulonge to Carillon are expected to plateau or slowly decline depending on weather. Risk of further increase in levels over coming weeks is higher from Mattawa to Lake Coulonge given the high snowpack remaining in the northern part of the basin.