Ontario won't shut down its worst polluting power plant as early as it planned because it still needs the power the old, coal-fired generator produces.

The giant Nanticoke plant on Lake Erie produces 4,000 megawatts of electricity and was to have been closed in 2007. But now, it probably won't close until 2009 according to provincial Energy Minister Dwight Duncan.

Duncan said the province's three other remaining coal-fired plants �?the Lambton plant south of Sarnia, Atikokan in northwestern Ontario and a plant in Thunder Bay �?would close on schedule in 2007.

Nanticoke's plume contains 14 per cent of the province's small particulate matter, a prime cause of asthma attacks, heart attacks and bronchitis, according to the Ontario Clean Air Alliance.

The province's coal-fired plants cause up to 668 premature deaths, 928 hospital admissions and 1,100 emergency room visits each year, an analysis released in April said.

Duncan attributed the Nanticoke delay to upgrading the transmission grid in southwestern Ontario. He had warned earlier that the province needs to find clean-air energy alternatives to replace the coal-fired plants before they could be closed.

The overall plan would see greenhouse gas emissions cut by up to 30 megatonnes a year, almost the same as taking seven million cars off the road. It would contribute almost half of Ontario's requirements under the Kyoto Protocol.

Nanticoke supplies about one-fifth of the province's energy requirements on a given day. Using the average household demand of 10-20 kilowatts, Nanticoke can supply power to up to 400,000 homes.

The Nanticoke announcement may add to the image of Ontario Premier Dalton McGuinty as a promise-breaker. His Liberal government budget last year broke a pledge not to raise taxes.