System at a Glance
River Flow — Real-Time Stations
Infrastructure Context
Britannia WTP — Ottawa River primary source
The Britannia Water Purification Plant, located on the Ottawa River at Britannia Beach, is Ottawa's primary water treatment facility. At 680 ML/day capacity, it handles approximately 90% of Ottawa's water supply, drawing directly from the Ottawa River.
The Ottawa River carries drainage from a vast watershed spanning Ontario and Quebec — including agricultural runoff from the Quebec highlands, industrial effluents from upstream communities, and seasonal sediment from spring snowmelt. The river is internationally shared; water quality decisions upstream in Quebec directly affect Ottawa's intake conditions.
The system has no source water reservoir — both WTPs draw directly from their respective rivers. A major contamination event on the Ottawa River would force full reliance on the Rideau River, which can supply only ~25% of total demand.
The Rideau River cyanobacteria problem
The Rideau River, which supplies Ottawa's Lemieux Island WTP, experiences recurring blue-green algae (cyanobacteria) blooms in late summer and early fall. The blooms are driven by nutrient loading from agricultural runoff and urban stormwater throughout the Rideau watershed.
During bloom events, the Rideau River intake requires additional treatment — including activated carbon for taste and odour removal, and careful monitoring for algal toxins (microcystins) that conventional chlorination does not fully remove.
The frequency and intensity of Rideau River blooms is increasing with climate change — warmer water temperatures and longer growing seasons create more favourable conditions for cyanobacteria. This makes the secondary source progressively less reliable during the late-summer period when conditions are historically most challenging.
Ottawa Water System
Station Map
River Flow Profile
Full Water Cycle