Twice in the past three months, missteps by the Army Corps of Engineers have left boaters and rowers high and dry on the Chattahoochee River in north Fulton County.

Both times, the stream became unnavigable through the National Recreation Area in Roswell and Sandy Springs. Boating, rowing and fishing — the big draws of the river and a source of tourism for both cities — were impossible.

The Chattahoochee River National Recreation Area runs 48 miles, from Buford Dam at Lake Lanier south to Peachtree Creek in Atlanta and draws more than 3 million visitors a year, according to estimates from the National Park Service. But the 6 1/2-mile stretch from Ga. 400 in Roswell to Morgan Falls Dam in Sandy Springs draws some of the largest crowds of boaters, kayakers and fishermen.

In July, the river sank to its lowest level in years near Morgan Falls when the Corps failed to perform a scheduled release at Buford Dam. Corps officials blamed a miscommunication. The level fell again Thursday when a siren malfunction at Buford Dam delayed a release for nearly 12 hours.

“[This is one of the busiest national recreation areas in the United States,” said Patty Wissinger, superintendent of the Chattahoochee River National Recreation Area. “Even on weekdays during the off-season, there can be several hundred people who are out using the river throughout the 48-mile park. In the summer, there may be thousands.”

And it is more than kayakers looking for a rush.

“It not only affects us but about 400 high school and college rowers who are trying to get out there,” said Charlie Freed, vice president of the Atlanta Rowing Club in Roswell.

Kim Sanders, facilities manager at the club, said she had to turn away scores of rowers who had come out to practice during the July incident and another dozen on Thursday.

“You’ve got a competitive racing team that is unable to practice. You’ve got casual rowers unable to use the river for recreation,” she said. “It’s like being a bicyclist and not being able to go bicycling.”

The Parks Service hears about it every time the river drops but has no control over river levels.

The corps releases water from Buford Dam to meet flow requirements for the Chattahoochee River at Peachtree Creek, 12 miles downstream of Morgan Falls Dam. It’s here where Cobb County and Atlanta have intake pipes to supply their water systems.

The Corps said backup contacts and phone numbers have been circulated to avoid any other incidents.

Lisa Parker, spokeswoman for the Corps’ regional office, said crews continue to perform preventive maintenance on the siren at Buford dam.

The Corps is in the process of updating its operations manual for Lake Lanier and Buford Dam and is inviting public comment on its responsibilities relating to recreation, navigation, fish and wildlife.

Comments can be made online at http://www.sam.usace.army.mil/pa/acf-wcm/form.htm or by emailing acf-wcm@usace.army.mil.