A herd of bison swim across the Yellowstone River in Yellowstone National Park, Wyoming in this June 21, 2011. (Jim Urquhart/Reuters)

This post has been updated

A House panel’s green light Thursday to lift longstanding restrictions on kayaks, rafts and other “hand-propelled” watercraft on rivers and streams in Yellowstone and Grand Teton national parks has opened a new front in the battle between environmentalists and tourists.

Legislation pushed by Rep. Cynthia Lummis (R), Wyoming’s lone House member, passed the Natural Resources Committee on a party-line vote and now heads to the House floor.

The bill requires the National Park Service to study a combined 6,500 miles of waterways in the parks to assess the impact on fish and wildlife of expanding paddling there. But with no study, park visitors could travel down 450 miles of rivers and streams thanks to a last-minute amendment that passed the committee.

Lummis has been backed by recreational paddling groups who have long wanted to expand access to the waterways in Yellowstone and Grand Teton, two of the crown jewels of the national park system.

Kevin Colburn, national stewardship director for American Whitewater,  a river stewardship and access group, said the group supported an earlier effort by Lummis to open the waterways to non-motorized boating that failed in the last Congress. He said they have not taken a position on the bill that cleared the committee Thursday.

“Our position has evolved,” Colburn said. “The paddling community is of two minds on the issue this time.”

Conservation and angling groups are decrying the bill as a disaster for the environment on the grounds that opening some of the parks’ most pristine, remote corners to visitors could help the spread of invasive aquatic plans, damage native trout habitat and disrupt a prime habitat for endangered grizzly bears.

“These are our prized national parks,” said Kristin Brengel, legislative director for the National Parks Conservation Association, a leading preservation group. “The majority of their visitors want to hear that we’re protecting the wildlife. There are lots of other opportunities in the region for paddling.”

Commercial raft tours would still be prohibited along the newly opened waterways, but pack rafts carrying multiple people would be allowed.

Thousands of paddlers every season already visit areas in Yellowstone and Grand Teton where non-motorized vessels are not banned, although they are limited. That includes 60,000 paddlers a year who paddle down the Snake River through Grand Teton, and more than 2,000 permits for non-motorized boating in Yellowstone, according to the National Park Service, which testified before Congress last year on a similar bill that passed the House.

Kathy Kupper, a park service spokeswoman in Washington, said the agency does not take a position on legislation unless it is asked to testify. It was not asked to on the current measure.

But officials testified last year that under such a change, park administrators would be prevented from using their professional judgment to decide where vessels should be allowed.

The legislation has stirred many passions locally, with bloggers and columnists weighing in.

“…a small group of mostly Jackson Hole pack rafters insists upon making a personal conquest out of Yellowstone National Park,” Todd Wilkinson wrote in the Jackson Hole News & Guide.

“To exact revenge against Yellowstone Superintendent Dan Wenk, who rejected their demand to overturn a historic paddling ban on park rivers, they went to Congresswoman Cynthia Lummis, a Wyoming Republican who has racked up one of the worst environmental voting records on Capitol Hill…”

“Do a few pack rafters really claim they know better than the combined wisdom and experience of those lined up against them?”