First Nations leaders are heading to Washington on Monday to persuade officials to reject a pipeline project that would pump more "dirty oil" from Alberta into the United States.

The delegation is composed of two community leaders from Canada and another from Minnesota.

Francois Paulette, of the Smith’s Landing Treaty 8 First Nation, will explain to U.S. politicians that pollutants from the oilsands already affect more than 30 downstream First Nations communities.

Increasing oilsands production would make matters worse, he said.

"I think the Americans really need to see the big picture," the former Dene Nation chief said in an interview from Fort Smith, N.W.T. before leaving for Washington.

"I hope that they rethink their plan of engaging our pipeline."

In fact, Paulette wants a moratorium on the Keystone XL pipeline expansion.

"The oil that they're buying is the dirty oil," he said.

Paulette will be joined in Washington by George Poitras, a former chief of Alberta's Mikisew Cree First Nation, and Marty Cobenais, a member of the Indigenous Environmental Network.

From Monday until Wednesday, the leaders have meetings scheduled with the State Department, a White House environment council, the Department of Interior, the Canadian Embassy, and congressional offices.

Paulette said he will point to the findings of a recent study that linked oilsands operations to high levels of lead, mercury and other heavy metals in the Athabasca River system.

Last week, a group of scientists and aboriginals asked Ottawa to step in to see if pollution from the oilsands is making fish sick.

Paulette said more and more downstream catches — a network that stretches 1,600 kilometres — contain fish with soft, mushy flesh.

"It's a big mess, but this mess is reaching the Arctic Ocean and we need to do more," said Paulette, whose meetings are sponsored by the Pembina Institute and the Natural Resources Defense Council.

"The whole way of life of the indigenous people is disrupted."

Keystone XL has been approved by Canadian regulators, and is now awaiting a green light from the U.S. State Department. The TransCanada Corp. pipeline would reach all the way to the U.S. Gulf Coast.

Earlier this month, First Nations and environmental groups met with Nancy Pelosi, Speaker of the U.S. House of Representatives, during her visit to Canada.

They urged the powerful politician to demand cleaner oil from Canada and to call on Ottawa to take a tougher stance on the oilsands industry.