Water quality in the Ottawa River basin is considered good overall as a result of the high velocity of the water and the numerous wastewater treatment plants that have been established. Most problem areas are localized, such as around densely urbanized areas. The Ottawa River’s many tributaries affect the overall water quality of the river itself. Despite localized problems, the majority of the Ottawa River is considered suitable for recreational uses such as swimming and fishing.

Water quality is generally considered good in the Ottawa River between Lake Temiskaming and the Gatineau River. Around Lac Coulonge, the water is considered polluted. Water quality in this stretch has been improving since the 1980s, as is the visible appearance of the water, which is affected by solid waste in the water as well as the water’s colour. Historically, PCBs and DDT have been found in high levels between Chaudiere and Carillon. Nickel and copper are heavy metals found in small concentrations along the river.

Water quality above Lake Temiskaming is considered good, although the water table has been polluted in numerous places due to the absence of adequate septic tanks because of the clay-like soil. Wastewater treatment around Ville-Marie has improved water quality for swimming. In the upper stretches, wastewater from industry such as paper mills decreases water quality. The presence of cottagers in lakes within the river basin tends to lower the quality of the water.

The water quality of the Ottawa River is extremely important, as it is the source of drinking water for many local communities. The City of Ottawa is the heaviest of these users, drawing 341 million litres of water from the river each day at the Britannia and Lemieux Island water purification plants.

For more information on who is monitoring the water quality of the tributaries flowing into the Ottawa River see your local watershed: Gatineau Water Quality, Lievre Water Quality, Mississippi Water Quality, Rideau Water Quality, and South Nation Water Quality.

Also the Ottawa Riverkeeper Water Quality webpage

Source: Ottawa River Background Study by the Ottawa River Heritage Designation Committee