Prime Minister Stephen Harper touted his government’s environmental record on Saturday as he announced plans to increase the size of Canada's newest national park, the Rouge National Urban Park in the Greater Toronto Area.

Speaking in Pickering, Ont., Harper said his government plans to add 21 square kilometres of land (5,000 acres) to the park for trails, campgrounds, and other outdoor activities. The area will also include tracts of farmland and archeological sites.

"Today's announcement means that Canadians for generations, here in the GTA and across the country, will have the opportunity to learn more about Canada's story," Harper said. "They will be able to experience the greatness of this country that begins with nature."

The Conservatives originally announced their intention to create the park in 2011, but legislation only came into force in May.

The park sits on a patch of land that stretches across the cities of Toronto, Markham and Pickering. The area was originally set aside for the construction of an airport under Pierre Elliott Trudeau's Liberal government, but plans never materialized.

On Saturday, Harper repeatedly referenced the failed airport plans, blaming Trudeau for "crippling vibrant communities" and delaying economic development in the region.

Harper also addressed critics who oppose Conservative environmental policies, saying his government has worked to preserve the environment by establishing six new parks, while expanding others.

"When you put all that together, this is an environmental record of which this country can be very proud," he said.

In the past, the government has faced direct opposition against its plans for Rouge Park.

Critics have said the initial plans did not include proper environmental protection measures, threatening the Rouge Valley's natural ecosystem.

In February, Ontario's Minister of Economic Development, Employment and Infrastructure, called the bill  "a joke."

"We’re just not willing to pass on ownership of the land to a federal government that refuses to put in a strong enough piece of legislation to preserve it," Duguid said.

Duguid and others worried that legislation protecting the park did not "meet or exceed" standards set by policies, and that key areas of the valley, including the Rouge River, would be left unprotected. The province also raised concerns about farming practices in the park.

On Saturday, Harper called that criticism unfounded.

"The new Rouge National Urban Park will have the highest level of environmental protection," he said.