Starting Friday, the U.S. Army Corps of Engineers will reduce the amount water flowing from Lake Lanier, but not by as much as Georgia requested.

The move could keep as much as 64.6 million gallons of water a day in Lanier, or about as much as Gwinnett County withdraws from the lake during the winter. The corps took the same action during the last drought, in 2001 and 2002, to preserve water in Lanier, metro Atlanta's main source of drinking water.

Georgia Environmental Protection Division Director Carol Couch issued a statement saying she appreciates the corps' careful evaluation of her request to cut the water releases through April 30. In its evaluation, the corps agreed with EPD that sending less water down the Chattahoochee River will not compromise water quality as long as cool temperatures continue to raise the amount of dissolved oxygen in the water.

As the water warms, dissolved oxygen declines. Oxygen is an important indicator of water quality and is critical to river life.

On Feb. 11, Couch asked the corps to leave as much as 129.2 million additional gallons of water a day in Lanier. That would mean reducing the amount of water flowing down the Chattahoochee past Atlanta by more than one-quarter, to 355.4 million gallons a day.

In reviewing the request, the corps found it would violate a 1946 Congressional document that authorized the federal government to build Lanier's Buford Dam. That document stated the Chattahoochee should flow at a minimum of 420 million gallons of water a day past Atlanta.

More than 30 years ago, the state raised that minimum to 484.7 million gallons of water a day. The reason was twofold: for drinking water and to assimilate treated sewage. Metro Atlanta communities take their drinking water out of the river, and downstream they discharge treated sewage. The river water mixes with the treated sewage to further "clean" it as it moves downstream.

On most days since December, the corps has released only enough water from Lanier to meet metro Atlanta's water needs and the state's minimum required flow.