TORONTO -- A coalition of environmental groups has gone to Federal court demanding a judicial review of a positive environmental assessment involving one of Canada's largest nuclear generating stations.

Ecojustice and the Canadian Environmental Law Association -- representing Greenpeace Canada, Lake Ontario Waterkeeper and Northwatch -- claim the refurbishing and long-term operation plans for Ontario's Darlington Nuclear Generating Station haven't come under enough scrutiny.

The groups allege the Canadian Nuclear Safety Commission's approval of the environmental assessment is "invalid and unlawful" because it doesn't comply with the Canadian Environmental Assessment Act.

They claim the assessment that was approved in March failed to consider a number of issues involved in refurbishing the station, including potential effects on Lake Ontario's fisheries and unpredictable major accidents.

The Darlington station, operated by Ontario Power Generation, is a four-unit facility located in Clarington, Ont., about 70 kilometres east of Toronto.

The refurbishment is expected to allow the station -- which provides about 20 per cent of Ontario's electricity needs -- to continue operating until 2055.

The Canadian Nuclear Safety Commission reports to Parliament through the Ministry of Natural Resources.

The environmental groups have sent their notice of application to the Attorney General, the Minister of Fisheries and Oceans and Ontario Power Generation.