The operators of Buford Dam at Lake Lanier received approval Monday to hold on to more water for metro Atlanta.

The U.S. Fish and Wildlife Service concluded that a proposal for Lake Lanier and other Chattahoochee River reservoirs to store more water and release less will not be a threat to endangered and threatened fish and mussels downstream.

The U.S. Army Corps of Engineers put the plan, a response to North Georgia's continuing record-breaking drought, into effect Sunday.

"We can hold or retain more water within the [river] basin than we could previously," said Col. Byron Jorns, commander of the corps' Mobile district, which is responsible for federal projects on the Chattahoochee.

Previously, the five reservoirs were permitted to store 30 percent of the inflow into the river basin.

The proposal, announced in April, bumps the storage rate to 50 percent.

The Fish and Wildlife Service determined that the additional retention, while it will have adverse effects on Gulf sturgeon and three varieties of mussels in the Apalachicola River and bay that are either endangered or threatened, won't jeopardize their existence.

The Chattahoochee and Flint River form the Apalachicola River, which runs to the Gulf of Mexico.

The corps needed the Fish and Wildlife Service's consent to go ahead with its Revised Interim Operations Plan that will govern the release of water from the reservoirs for the next five years.

A new plan to replace the interim version is in the works. It is not certain when it will be completed.

Given the drought conditions, Lake Lanier still will need plenty of rain to fill up.

The corps said under dry conditions this summer, the lake level could fall 2 feet to 7 feet from its current level.

The change in operations drew criticism with the announcement Monday.

A policy expert at the Environmental Defense Fund, a nonprofit environmental policy and research organization, said the decision is bound to create more litigation and controversy.

"The need for sustainable management of this critical tri-state river basin should not be made on such a piecemeal basis," Mary Kelly, vice president for rivers and deltas, wrote in an e-mail.

Pam Stevens, the Atlanta Regional Commission's environmental planning director, said Monday that the plan isn't enough.

"It still doesn't allow Lanier to refill," she said. "You've got a reservoir that 3.5 million people depend on."

Some down river in Florida aren't very happy, either.

"A continued reduction in flows to the Apalachicola River during the next five years places the economic and environmental future of an entire region at risk," Florida Gov. Charlie Crist said in a statement.