A tear in a seam of an inflated rubber dam sent millions of gallons of water gushing from Tempe Town Lake, authorities said Wednesday.
Tempe City Manager Charlie Meyer said police determined no criminal activity was involved in the failure of a 16-foot-high section of the inflated rubber dam near Arizona State University's campus.
"What we believe we have is a straight-line tear," which would indicate it happened along a seam line, Meyer said.
Mayor Hugh Hallman said the desert environment, with its blazing sun and 110-degree temperatures in the summers, combined with the cooler winters, likely led to the rubber dam's deterioration. It gave way at about 10 p.m. Tuesday, sending water flowing into the normally dry Salt River.
"All of a sudden, we heard this ka-boom and the ground started shaking," said 13-year-old Lukas Henderson, who was biking on the north side of the lake with his sister and father.
Witnesses said the river filled as far as the eye could see within seconds, and small animals scrambled away from the floodwaters.
Warning sirens began wailing within minutes, and officers rushed along the riverbed to warn people of the approaching water, particularly transients known to camp on the river bottom during the summer.
There were no reports of injuries, and authorities said no structures were in danger.
The 220-acre lake has hosted the swimming portion of several triathlons and is popular with rowers, sailors and fishers who take advantage of the urban water about eight miles east of downtown Phoenix.
The lake will likely be closed until the fall while the city makes repairs, Hallman said.
Tempe spokeswoman Kris Baxter-Ging said workers were speeding up an effort already under way to replace the dam's bladders. The project had been delayed earlier this year by winter flooding, she said.
The lake, which can hold up to 1 billion gallons of water and was first filled in 1999, has four inflatable dam sections on each end. They were supposed to last for 25 to 30 years.
However, Tempe officials determined in 2007 that Arizona's harsh climate was taking a toll on the rubber dams and they might have to be replaced soon.
The city inspects the dams about once a month and repaired two tears in 2002.