A proposal to loosen federal fish habitat protection rules threatens Canada's water quality, fisheries and its international reputation, scientists warn.

In a letter sent Thursday to Prime Minister Stephen Harper and Fisheries and Oceans Minister Keith Ashfield, a group of 625 scientists urged the government to abandon changes to the Fisheries Act outlined in an internal government document leaked late last week.

The document suggested the act is to be revised so Ottawa would be responsible for fish, but not their surrounding habitat.

The act currently requires projects such as oil pipeline and road culvert construction to show their plans will preserve fish habitat.

"Removing those provisions … would basically give proponents of projects license to do anything they pleased," said David Schindler, the University of Alberta ecologist who is the lead author of the letter.

Schindler said he and his colleagues fear the changes to the Fisheries Act will be attached to the upcoming federal budget as part of an omnibus bill. The budget is set to be delivered on March 29.

The proposed changes are of particular concern now, Schindler said, because the government is trying to push big projects such as the proposed Northern Gateway pipeline "where literally hundreds of fish-bearing streams would be crossed." The controversial pipeline would connect Alberta's oilsands with the port in Kitimat, B.C.

Schindler said "very cumbersome" environmental approval processes can be streamlined by focusing on the relevant science. Currently, he said, the process involves a lot of "filler."

Schindler said the signatories of his letter include many national and international prize-winning scientists and the number of them supporting the letter indicates how important habitat protection is.

"If you look at any list of endangered species and species in decline, you'll find that 80 per cent of them are declining because people have destroyed their habitat," he said.

The Canadian Society of Ecology and Evolution and the Canadian chapter of the American Fisheries Society also sent letters expressing concern about the possible changes to the Fisheries Act.