PAGE, Ariz. — Caretakers of the Colorado River below the Glen Canyon Dam keep going back to one word when they talk about the health and well-being of the habitat and abundant resources along its 277-mile path through the Grand Canyon.

Balance.

For the hundreds of archaeological sites on or near the river. For the delicate ecosystem beneath the water's surface. For recreation and habitat along its shore. For generating power at the point where the Colorado slips from beneath the 710-foot dam. For resource conservation below the dam.

Balance.

It's a word that pops up frequently as scientists, biologists, park service officials, Native American tribal leaders and officials with the Bureau of Reclamation and Department of Interior all try to decide what's best for the river and riparian zones south of the dam.

As recently as last Friday, the scales tipped in favor of final approval for what the BOR is careful to say is a "high-flow" experiment — not a flood — that starts at the dam. For 60 hours beginning this morning, 41,000 cubic feet of water per second will flow from the dam's power plant, or pin stocks, and jet tubes.

The flow is supposed to move sediment built up on the river bottom to rebuild or repair beaches downstream. Before the dam existed, it was Mother Nature's job to take care of spreading sediment and beach maintenance. Another hope is for the $4.1 million experiment to help establish sustainable backwater habitat for species like the endangered humpback chub.

Similar experiments took place in 1996 and 2004. This week's high-flow release will gradually raise the level of the river by at least four feet in areas closer to the dam, which was completed in 1966.

Slowly, over several days, the river's level will return to normal. Then it will be time to start studying whether the experiment worked.

The goals are many. The monitoring and research will go on for months.

People like Scott Rogers, a fisheries biologist with the Arizona Game and Fish Department's research branch, want to know about effects like fish displacement due to the release of so much water at once. Researchers have been tagging fish, mostly rainbow trout, trying to get an estimate of their numbers. Then they'll track fish movements after the experiment.

"The fisheries look good right now," Rogers said while on a 15-mile boat ride Tuesday from Lee's Ferry to the base of the dam.

But outfitters and anglers have opposed the timing of the experiment, which will greatly increase the Colorado's velocity, raising fears that fish will disappear, at least for a while. Rogers said those fears are probably more based in perception than reality.