A controlled flood of the Grand Canyon due to start today has caused a row within the federal government's department of the interior, pitting environmentalists and officials of the national park service against their colleagues in the bureau of reclamation and the geological survey.

The flood, the third in the last 12 years, will see 40,000 cubic feet per second released from the Glen Canyon dam down the Colorado river, instead of the customary 13,000 feet. The "blowout" is intended to clear accumulated sand and sediment from the riverbed and encourage the restoration of sandy beaches and side pools critical to the survival of native species.

The construction of the dam in 1963, and the resulting creation of the 186-mile long Lake Powell upriver of the Grand Canyon, put an end to the cycle of spring floods that would naturally flush out the river. It encouraged non-native fish to thrive while accelerating the extinction of four native fish species.

But the flood, which has been promoted by interior secretary Dirk Kempthorne, has run into opposition. Opponents argue that the one-off flood will cause more damage than benefit, and that the decision to allow just one flood fails to mimic natural conditions and could leave endangered fish and sandbars diminished.

Officials with the parks service have accused the bureau of trying to push through the plan without allowing sufficient time for review. Grand Canyon national park superintendent Steve Martin said he was given just one day in mid-February to submit comments on the plan. His submission blasted the plan for being out of touch with the latest scientific information.

"It is not apparent where the 80 million dollars in research, conducted over the last 10 years has been used in this decision-making process," he wrote. "Our analysis shows that this document is not consistent with current best information."

He concluded that the lack of additional high flows floods after this week "could lead to impairment of the resources" of the canyon.

In comments to the Los Angeles Times on Monday, Martin suggested that the manner and timing of the flooding was intended to benefit the hydroelectric power companies that use the lake, and need to satisfy peak demand during the summer.

"The best time to get the most money for your hydropower is during peak energy demands, which is generally daytime hours and generally in the summer," he said.

Lawyers with the department of the interior battled to make Martin withdraw his comments to the review, fearing that a finding of "significant impairment" would lead to additional reviews, effectively blocking the plan.

But a geological survey official told the paper that the flushing would go ahead, pointing out that the agency had to take into account the entire economic profile of the dam.

Jeff Ruch of the environmental pressure group Public Employees for Environmental Responsibility said that the Bush administration was trying to protect its legacy. "In its last months, the Bush administration is trying to extend its control through the term of its successor - a dead man's hand throttling Colorado River management," he said. "When engineers and lawyers wrap themselves in ecological rationales, it is time to watch out."

The group also criticised an exclusive deal offered by the interior department to the NBC network to cover the flooding.

"This week's high-flow stunt is nothing but a green wash to mask another betrayal of the Grand Canyon by its political custodians," said Ruch.