Proposed changes to a federal law governing navigable waters would end its ability to protect tens of thousands of Canada's waterbodies, environmentalists say.

Amendments to the Navigable Waters Protection Act introduced as part of a sweeping budget implementation bill on Thursday limit its application to 97 lakes, 62 rivers and the three oceans that border Canada. That means construction of dams, bridges and other projects would be permitted on most waterways without prior approval under the act, which currently covers any body of water big enough to float a canoe in.

Transport Minister Denis Lebel said the changes are meant to reduce the red tape for municipalities and cottagers seeking federal approval for small projects such as culverts or lakeside docks. He said the purpose of the act is to minimize interference with navigation, adding that waterways not on the new list will be protected by other federal laws and by provinces and municipalities.

Story continues below advertisement

"Over time, the scope and application of a law that was designed to protect navigation has expanded to the point where it now applies to brooks, streams, ditches. So now, even the most basic foot bridges over small streams still require pages of paperwork," Mr. Lebel said on Thursday.

The list of the bodies of water that will be covered include the ones most frequently used for transportation, Transport Canada officials said, adding that it could be altered in the future.

The name of the act will be changed to the Navigation Protection Act, a move officials say recognizes its "historic intent" to focus on navigation, not water.

The changes garnered praise from municipal representatives, who said they would help pave the way for economic growth and infrastructure development.

But environmentalists and opposition MPs said changes to the act are part of a broader move by the federal government to weaken environmental oversight. The last federal budget bill dramatically overhauled the rules for environmental assessments, shifting responsibility to the provinces and ending reviews for small projects.

"The destruction of the Navigable Waters Protection Act and renaming it the Navigation Act is part of a consistent pattern of Stephen Harper trying to remove federal constitutional authorities for the environment," Green Party Leader Elizabeth May said on Thursday.

John Bennett, executive director of Sierra Club Canada, said the changes mean provinces, territories and municipalities could be responsible for assessing the impact of construction projects they want to build themselves – a shift he suggested could result in conflicts of interest.

Story continues below advertisement

"You need a government that's not directly involved to be the one looking over the shoulder," he said. "It's sort of a basic rule of fairness that the person who wants to do something isn't the one who's deciding whether it's a good thing to do or not."

The Federation of Canadian Municipalities, which supports the government's proposed changes, said it didn't see a problem with municipalities managing local project assessments without federal oversight.

"[Municipalities] are accountable to the citizens, they do thousands of projects every year that end up with potential impacts on the environment, so they've got to be careful and they are careful," said Brock Carlton, the federation's chief executive officer. "There's no benefit to being disrespectful in terms of environmental management."

Ms. May said some of the changes help to improve clarity in the act, including a move that would allow the Transport Minister to require the owner of an abandoned vessel to remove it from a waterway.