Rowing enthusiasts along the Chattahoochee River had to ditch plans for a day on the water Thursday.

For the second time in three months, river levels in Roswell and Sandy Springs dropped to a point where rowers couldn’t dip an oar, much less float a boat.

“We started getting complaints from visitors Thursday morning,” said Patty Wissinger, superintendent of the Chattahoochee River National Recreation Area. “Our own staff was out there, saying ‘Gosh what’s wrong with the river? Where’s the water?’ ”

Wissinger said she didn’t learn till later in the day, after making phone calls, that the U.S. Army Corps of Engineers had failed to release water through Buford Dam overnight.

Corps spokesman Pat Robbins confirmed late Thursday that the release was canceled when a warning siren at the dam malfunctioned.

“We did not release because we have no way of notifying people downstream,” he said, adding that the interruption did not affect any of the minimum-flow requirements downstream.

The corps bases its releases from Buford Dam on requests to meet flow standards for the Chattahoochee River at its confluence with Peachtree Creek 12 miles downstream of Morgan Falls Dam in Sandy Springs.

In late July, the river sank to its lowest level in years near Morgan Falls when the Corps failed to perform a scheduled release at Buford.

Thursday’s water levels at Morgan Falls dropped to their lowest point since the July incident, according to records from the U.S. Geological Survey.

Kim Sanders, facilities manager at the Atlanta Rowing Club in Roswell, said she had to turn away patrons who wanted to rent boats Thursday.

“One gentleman actually went home,” she said. “He took one look at the river and said he wasn’t taking his own personal boat out either.”