PHOENIX (AP) — An environmental group says the Glen Canyon Dam, a key Colorado River dam on the Utah-Arizona border, is being mismanaged by the federal government, threatening already endangered species for the benefit of power production.

The Grand Canyon Trust made the allegations in a federal lawsuit filed Friday in Phoenix. The suit names the U.S. Interior Department's Bureau of Reclamation, which operates the dam, which has created Lake Powell.

The Flagstaff-based group's suit claims the government releases water from Lake Powell in a way that benefits power production but destroys downstream habitat for native fish.

River flows in the Grand Canyon have been an issue for more than two decades. Before it was dammed in 1963, flows ranged from heavy springtime flooding that cleansed the river's sand and gravel bars to slow late fall flows.

The dam's steady releases changed that habitat, and combined with introductions of non-native fish like trout, native fish populations plummeted.

The government already settled one lawsuit that claimed the dam's operation failed to protect endangered fish in the Colorado River.

In early 2006, five other environmental groups sued, claiming the Bureau of Reclamation's dam operations were driving four endangered fish species, the humpback chub, razorback sucker, Colorado pikeminnow and bonytail chub, closer to extinction.

That suit alleged the government released water at unnatural temperatures, quantity, quality and frequency, depriving the Grand Canyon of sediment and needed nutrients.

The suit was settled later that year with an agreement that the government would intensely study the effects of the dam and prepare a plan by late next year that may recommend dam-operation modifications.

The new lawsuit alleges that the Bureau of Reclamation hasn't followed its existing 1996 dam operations plan that was designed to adjust river flows to avoid undue environmental damage.

"To put it bluntly, current flows from Glen Canyon Dam are in violation of federal law," said Nikolai Lash, senior program director at the trust.