Forecast for 2026-04-18

River conditions forecasts posted on 2026-04-18 by Ottawa River Regulating Committee

Water levels and flows continue to rise at all locations along the main stem of the Ottawa River as significant runoff from rainfall and snowmelt from the unregulated portion of the basin flow into the river. Reservoirs are retaining spring runoff to reduce flooding in the dowstream river system. Minor flood levels have been exceeded in most flood prone areas along the Ottawa River from Pembroke down to Carillon. Major flood levels from Lake Coulonge to Carillon may be exceeded over the next few days depending on weather. The minor and major flood levels are defined on the Home page in the Special Feature section. Levels should continue increasing over the next few days in all locations and start stabilizing on Monday. Our website Forecasts section provides expected water levels over a four-day horizon in several areas. Uncertain weather factors play into estimating peak levels over the coming week. On April 18 peak level estimates are generally above 2025 peak levels but below 2023 peak levels, as follows: Pembroke (113.05 m), Lac Coulonge (108.55 m), Chats Lake (75.55 m), Lake Deschenes (60.2 m), Gatineau -Hull marina (44.45 m) and Thurso (42.95 m). These exceed 2025 peak levels by 20 cm (Pembroke), 40 cm (Lake Coulonge), 30 cm (Chats Lake), 45 cm (Lake Deschenes/Britannia), 90 cm (Gatineau -Hull marina) and 65 cm (Thurso). Over the next two weeks, levels 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.