Brian Witte, Associated Press
Grand Canyon visitors ride a raft through the rapids. The National Park Service wants to increase the number of passengers.

PHOENIX — More river runners may soon be challenging the rapids of the Colorado River through the depths of the Grand Canyon, under a proposal by the National Park Service.

The agency wants to increase the total yearly passengers by 3,856 — from 22,461 to 26,317 — as part of a revised Colorado River management plan.

A panel of scientists, geologists, professors and consultants is considering increasing the passenger totals, while reducing the number and length of trips, as well as group sizes for some areas.

Some launches also may be shifted into nonpeak seasons. The number of months that nonmotor boats use the river could increase from three to six months.

"People will still have plenty of opportunities to go down the river, but there will be some changes in the way the system operates," said Rick Ernenwein, who is heading up the plan.

The public has until Jan. 7 to comment on 13 alternative plans for the 277 miles of Colorado River from Lees Ferry, south of Lake Powell, through the Grand Canyon to the edge of Lake Mead. A group of experts will then analyze the comments before submitting a final environmental impact statement.

A final environmental statement could be completed by spring, Ernenwein said.

Once the regional director of the Park Service approves a plan, some parts could be implemented immediately, Ernenwein said. Others could take a year or longer.

Eight alternatives are being considered for the river from Lees Ferry to Diamond Creek, through the heart of Grand Canyon National Park. This is the section where the majority of river trips are conducted.

On another section of the river stretching from Diamond Creek to Lake Mead, the Park Service wants to lower pontoon boat use and cap the number of passengers at 150 daily.

The park wants to increase the overall operations in this area while reducing the group sizes. It would also like to eliminate peak use by spreading trips out. Five alternatives are being studied.

Experts began discussing in January 2003 on whether to alter the number of recreational and commercial river runners allowed to use the Grand Canyon.

A panel of experts then came up with suggestions about how to better manage the corridor.

The main purpose of the 10-year plan is to protect the natural and cultural resources, while allowing as many people as possible to enjoy the area, Ernenwein said.

"If we don't protect the resources in the river corridor, it will change the type of experience people have," Ernenwein said.

Some environmentalists are critical of the Park Service's plan. David Haskell, policy director for Living Rivers, a group that promotes river restoration, said it doesn't go far enough.

"We feel like the Park Service has fallen short, in particular in not addressing the group size of commercial groups," Haskell said.

Besides further decreasing the commercial group sizes, Haskell said the Park Service needs to phase out or stop allowing motorized boats on the river.

"It's a money issue rather than a resource protection issue," Haskell said.