WASHINGTON — The mountain lakes in the backcountry of Washington state’s North Cascades National Park are still covered in ice. The thaw usually doesn’t come until early July. This year, however, a deadline comes along with the thaw.

Unless Congress acts, the lakes won’t be stocked by volunteers racing the clock through the wilderness with 5-gallon plastic containers of rainbow, cutthroat and golden trout strapped on their backs.

The size of Rhode Island, the North Cascades is the only national park where fish are still planted. The lakes, many carved out by glaciers and fed by cold glacial water, didn’t have fish in them until the planting started roughly a century ago.

National Park Service rules prohibit the introduction of non-native species, and it will start enforcing them July 1 in the North Cascades.

“We are the last park,” said Chip Jenkins, the park’s superintendent. “If we are to continue to do something unique, Congress will have to authorize it.”

The dispute is just the latest flash point in the broader debate between those who think that the national parks and wilderness should remain pristine and untouched by humans, and those who think that increased recreational opportunities should be allowed as long as they don’t harm the environment.

Washington state Rep. Doc Hastings, the top Republican on the House Natural Resources Committee, has introduced legislation to allow planting in the North Cascades to continue. He has support from virtually all the state’s delegation in the House of Representatives, including leading Democrats. Hastings said he hoped that his bill would pass the full House in the week after Congress returned from its Memorial Day recess.

Though Hastings said Washington state’s senators, Democrats Patty Murray and Maria Cantwell, supported his measure, they haven’t introduced a companion bill in the Senate. Murray’s and Cantwell’s offices declined to comment.

“If the (July 1) deadline helps pass it, I have no trouble with that,” Hastings said, “but the problem in the Senate is finding time to do it. Maybe the deadline will help with that.”

Sandy McKean, a past president of Washington Trail Blazers, a group that supports alpine fishing, has hauled fish to the lakes in the North Cascades for 15 years. He said that some members of the group had been doing it for 50 years.

McKean said the National Park Service set the July 1 deadline because it was worried it might get sued if the planting continued without congressional authorization. He added that the national parks are filled with trails and people climb rocks, gather mushrooms, view birds and wildflowers, and ride horses.

Opponents say McKean and his group are “elite” fishermen, and the park service ought to ban the stocking program outright.

“This is a national park,” said Dave Fluharty, a board member of the North Cascades Conservation Council. “There are 400 other lakes they could be fishing in. The lakes in the park need to be left alone.”