The National Water Research Institute (NWRI), headquartered at the Canada Centre for Inland Waters, is a directorate of Environment Canada's Environmental Conservation Service. The institute is Canada's largest freshwater research facility, with over 300 staff, including aquatic ecologists, hydrologists, toxicologists, physical geographers, modellers, limnologists, environmental chemists, research technicians and experts in linking water science to environmental policy.

NWRI has major facilities in Burlington, Ont, and Saskatoon, Sask, and networking offices in Victoria, BC, Fredericton, NB, and Gatineau, Qué. In partnership with the Canadian and international science communities, NWRI conducts a comprehensive program of ecosystem-based research and development in the aquatic sciences, generating and disseminating scientific knowledge needed to resolve environmental issues of regional, national or international significance to Canada, and to sustain our natural resources and freshwater ecosystems (see also Water Pollution).

NWRI delivers its programs through a number of branches focusing on aquatic ecosystem impacts, protection and management research, monitoring, science liaison and research support. It also comprises the National Laboratory for Environmental Testing (NLET) and, since 1974, hosts the program office for the United Nations' Global Environment Monitoring System (GEMS/Water), a multi-faceted water science program oriented towards understanding freshwater quality issues throughout the world.

As well as international projects, the institute has research sites across Canada, from remote locations in the vast Mackenzie Delta in the Northwest Territories to the waterfront in the city of Toronto; from farmland in Saskatchewan and Ontario to isolated sub-Arctic lakes; and from national parks to sewage treatment plants.