Editor's note: This story has been updated with the cause of the malfunction at Longhorn Dam.
If you happened to be near Austin’s Lady Bird Lake on Monday, you might have noticed it looked different.
The lake level, which usually stays constant year-round, had dropped by about 2 feet, exposing stretches of muddy, sometimes smelly, shoreline.
The cause was a problem at Longhorn Dam on Sunday night.
"We experienced a control system malfunction at Longhorn Dam, which affected the operation of the bascule gate, a movable drawbridge-like gate allowing precise water level control,” Austin Water’s Martin Barbosa said in an email Monday night. "It was an isolated incident, and the root problem is now corrected.”
The Longhorn Dam was built in 1960 to create a reservoir to serve the Holly Power Plant. The power plant is now gone, but the reservoir, now commonly known as Lady Bird Lake, remains as an iconic city amenity.
The dam’s age and maintenance has sometimes been a challenge for the city.
In 2013, a massive flood led to a problem with the dam gates that threatened to drain Lady Bird Lake of water.
After that, the city invested in upgrading the dam. Austin Energy, which had been responsible for dam management since the days of the Holly Power Plant, also transferred operations to Austin Water.
The area around the dam has been buzzing with heavy equipment as contractors work to install a new “wishbone bridge” and pedestrian tunnel nearby. But Austin Water says that construction had nothing to do with the malfunction.
When asked for details about what happened, the utility said ants were responsible.
"Ants intruded on the instrument panel, shorting it out and tripping a circuit breaker," Barbosa wrote in a followup email Tuesday. He said that caused the water gate to fall "partially open."
Barbosa did not reply to a question about how much water had been lost due to the malfunction, writing only that the water that drained out will count toward "the planned release that was scheduled later in the evening on Sunday."
Austin Water regularly allows water to pass through the dam to meet downstream environmental and agricultural needs.
According to data from the Lower Colordado River Authority, the lake level dropped about 2 feet before it started to rebound Monday night.
The surface area of Lady Bird Lake covers approximately 468 acres, indicating that a significant amount of water went downstream due to the gate opening.
Austin Water works in conjunction with the LCRA, moving water through the Tom Miller Dam upstream and the Longhorn Dam downstream, to maintain the lake level at around 428 feet above sea level.
By Tuesday morning the lake level had returned to normal.
