A few hundred protesters turned up at Queen’s Park in Toronto on Friday to protest a massive limestone quarry proposed for development north of Orangeville.

The mega-quarry would span more than 800 hectares — about one third the size of downtown Toronto — and create a crater one and a half times as deep as Niagara Falls.

Those opposed to the project are concerned about losing a massive swath of rich farmland and are also worried about the quarry’s effect on the water table.

"Digging up 2,000 acres of some of the richest agricultural land in the country. This is just a bad idea," said cattle rancher Carl Cosack, who attended Friday’s protest and who owns property in the area. "Everyone downstream is affected.”

The U.S. company behind the proposal, Highland Companies, said they've listened to these concerns and are taking steps to protect the environment.

A few hundred protesters gathered at Queen's Park to voice their opposition to a proposed limestone quarry planned for of farmland north of Orangeville. (CBC)

The company says the limestone quarry would provide an essential supply of aggregate, which is used to build everything from homes to roads.

In a statement, the company added: "The design of the proposed quarry balances environmental protection while also responding to market conditions."

But protesters say no amount of aggregate is worth destroying such rich farmland.

"We're nourished by that land,” said protester Paul DeCampo. “So it's logical that we would stand up and protect it."

The quarry project has become an issue for politicians leading up to Thursday's provincial election.

In early September, just prior to the start of the campaign, Liberal Leader Dalton McGuinty ordered an environmental assessment into the project.

Progressive Conservative Leader Tim Hudak said Highland Companies should "go back to the drawing board" and amend the project to take into account residents' concerns.