The equipment is deepening and narrowing the channel and nudging boulders and tree trunks into place along about one-mile stretch of the river at Cottonwood Campground. The goal is to create better hangouts for fish.

"This stretch of the river was wide and shallow," said John Hansen, a wildlife biologist with the Bureau of Land Management as he watched the bulldozer and track hoe operators work last week. "The channel right here was maybe 150 feet wide and 8 to 10 inches deep. Now it's like 90 feet wide and four feet deep."

Boulders, combined with the trunks and root balls of cottonwood trees lodged in the river, break the flow of water, creating eddies and poolson their downstream side.

"There will be prime habitat for fish," said Hansen, who is based in Farmington. "In the eddies, fish will spend less energy fighting the current. They can wait there and when they see something to eat, they can dash out and grab it."

Tom Knopick, co-owner of Duranglers Flies and Supplies of Durango, hasn't seen the current project. But such work holds two benefits, Knopick said.

"It creates fish habitat so there are more fish, but it also increases the velocity of water so more sediment is transported out of the fishery," Knopick said.

When sediment accumulates there are fewer bugs that fish eat, and so there are fewer fish, Knopick said. Over the past 25 years, development has disturbed more terrain, allowing an increased amount of sediment to be carried into the San Juan from tributaries, Knopick said. In the same period, he said, flows in the San Juan have decreased in response to increased demand for water.

"I can't remember flows below 1,000 (cubic feet per second) until recent years," Knopick said.

Navajo Lake State Park borders the south side of the river where the work is being done. The Bureau of Land Management manages the north side of the river.

Hansen said the channel work - being done by Adobe Contractors of Bloomfield - must be finished this week while the flow in the San Juan River is still reduced to 250 cfs. Starting at 4 p.m. today, the flow from Navajo Dam will be increased to 750 cfs.

The federal Bureau of Reclamation, which controls water flow out of Navajo Dam, agreed to reduce the release of water from Navajo Dam for two weeks to accommodate the channel construction work.

Numerous private businesses as well as federal and state agencies have contributed to the current $70,000 fishery project, Hansen said.

Hansen said the configuration of boulders and tree trunks in the 4,600-foot-long project looks a little more natural than the work done for two similar projects upstream.

The upstream projects, which begin at Navajo Dam and together cover about half the 1.75 miles of improved fish habitat, are known as "quality waters" where only catch-and-release fishing with artificial flies is allowed. Anglers can keep only one fish and it must be at least 20 inches long.

"People come from around the world to fish there for rainbow and brown trout," Hansen said.

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