Enough water to serve metro Atlanta and beyond can be pulled from Lake Lanier, according to an updated document governing the river basin straddling Georgia, Florida and Alabama.

But “the downside of it is that water has to come out of Lake Lanier, which means the lake levels will take a hit,” Lake Lanier Association’s new president, Wilton Rooks, said in an interview last week.

“And that’s acknowledged in the water control manual. They categorize it as slightly adverse — that’s sort of in the eye of the beholder, I guess.”

The Army Corps of Engineers’ updated water manual, released earlier this month, spells out operations for the Apalachicola-Chattahoochee-Flint River Basin.

The issue will be “how do we navigate into the future with minimizing the impacts on Lake Lanier,” Wilton said. “There are two ways to do it. One is you consume less (water) and (the other is) you return more.”

Another help would come from raising Lanier’s full pool level to 1,073 feet above sea level from 1,071 feet — a move that’s been long promoted by lake advocates.

“We hope it will be considered,” Rooks said.

Continued, and perhaps strengthened, conservation efforts also would help.

But “on the return issue, there’s a lot that can be gained there,” Rooks said. “That’s a factor that could be looked to bring more water back to the rivers and Lake Lanier.”

Georgia Department of Natural Resources spokesman Kevin Chambers said Georgia does return “a large percentage of the withdrawn water” to the basin, “so the impact is very limited.”

He said the percentage returned was 70 percent in 2011 and is projected at 75 to 79 percent for 2050.

Overall, Georgia got good news in the water manual, which hadn’t been updated since the late 1950s, the early days of Lake Lanier.

The manual also accounts for massive development in metro Atlanta — growth that’s expected to continue and spread.

Corps documents released earlier this month, including a final Environmental Impact Statement, show the agency has granted state requests for 242 million gallons per day in gross withdrawals from Lake Lanier and releases from Buford Dam to support downstream withdrawals of up to 379 million gallons per day.

The corps says it also is complying with the 11th Circuit Court of Appeals’ 2013 order, which authorized 705 million gallons per day in withdrawals “without jeopardizing downstream needs,” Chambers has said.

By comparison, the withdrawals in 2011 were 115 million gallons per day from Lanier and 246 million gallons downstream from Buford Dam.

Jason Ulseth of the Chattahoochee Riverkeeper has said that basically, the corps “is giving the metro Atlanta region the amount of water that they have requested through 2050 — either from Lake Lanier directly or from the Chattahoochee downstream from Buford Dam.”

Dan Tonsmeire, who heads Apalachicola Riverkeeper, said last week that the corps has said it is allocating water having “minimal impact” to the Apalachicola Bay in Florida.

But he believes “for the (corps) to ignore all the impacts in all the changes they have made in operations is short-sighted — and it’s incomplete. It just makes their answers wrong.”

“The bay collapsed in 2012, and they completely ignored that fact,” Tonsmeire said. “They didn’t even look at the bay. They looked at (a gauge) 78 miles upriver from Apalachicola.”

On the other hand, Katherine Zitsch, natural resources division manager for the Atlanta Regional Commission, has said she is “pleased that the long-term water supply needs of the Atlanta region will be met, as having a secure source of water is incredibly important to metro Atlanta’s future.”

“The Metro Water District is mindful that these precious resources are shared and is proud of our aggressive water conservation efforts that have dramatically decreased water usage in the region.”

Another issue to watch will be the outcome of a Florida lawsuit against Georgia over alleged “overconsumption” of water, leading to an ecological disaster in the Apalachicola.

A monthlong trial between the states ended Dec. 1 with a special master, Maine lawyer Ralph Lancaster, imploring both sides to negotiate a settlement.

He was appointed by the U.S. Supreme Court to make a recommendation to resolve the matter. The Supreme Court will have the final say in the coming year.