The water level at Lake Lanier will be lower for July 4 than it has been on Independence Day since it was built in the 1950s and the federal agency that operates the lake has issued a warning to holiday revelers.

"The shallower water conditions could expose sandbars or stumps to those swimming or boating," Corps spokesman E. Patrick Robbins said in a statement this week.

Vino Wong/AJC (ENLARGE)

A boat dock ramp now sits on dry land at the Shoal Creek cove area at Lake Lanier on Friday (June 27).

• Latest Photos: July 4 warning for Lanier • Photos: A shallow Lake Lanier can be hazardous DEALING WITH THE DROUGHT: • Can I water? Here are the rules • 10 tips to save water • Map: Heavy demands on our water RELATED: Georgia's hopes fading for reversing water ruling  Southeast must adapt for drought, report says  Lawn sprinklers can create icy roads: Turn them off  Lake Lanier to hold more water after feds decision  Drought saps lakes, tightens grip on north Georgia  • More on coping with the drought

"Boaters should be cautions as declining levels may reduce clearance over underwater obstructions."

Lanier is nearly 15 feet below full, at an elevation of 1,056.2 feet above sea level. The current record low for July 4 was set during another bad drought in 1988, at 1,061.2 feet above sea level or five feet higher than it will be this year.

According to the corps, only two of 39 public docks are useable and only 12 of more than 100 lanes at public boat ramps are useable.

Lanier has also lost swim areas. About 6,500 acres that were once under water are now dry, or about 18 percent of the lake's surface.

The corps expects Lanier to drop another foot by July 25.

Lake Allatoona, metro Atlanta's other popular corps-operated lake for fishing, swimming and boating, is in much better shape. That lake, northwest of Atlanta, is less than two feet below its full level.

Forecasts for the lake levels are on the web site for the Corps' Mobile District Water Management Section at water.sam.usace.army.mil. The corps also operates a toll-free voice phone system that provides daily lake level readings at 1-888-771-4601.