Officials say several boats sank on the lake during a parade in support of Texas state President Donald Trump in the November election.
Officials say a large number of vehicles collided head-on at Lake Travis near the state capital, Austin, causing flooding.
The images showed boats with Trump campaign flag maneuvers in nearby quarters.
Media say people were rescued from the water, but there were no immediate reports of injuries.
The event, called the Lake Travis Trump Boat Parade, was held on Facebook and was attended by more than 2,600 people.
An investigation has been launched and there is no evidence of an intentional act, said Kristen Dark, a spokeswoman for the Travis County Sheriff’s Office.
“We answered several calls from boats in trouble, many of which sank,” he said. “We had an exceptional number of boats on the lake today … when they all began to sail at the same time, they produced significant waves.”
The incident took place in the U.S. On Saturday, Labor Day became a weekend at around 12:00 (17:00 GMT). The event page said the boats were asked to drive at 10mph (16 km / h).
Paul Yura of the National Weather Service in Austin / San Antonio told the Associated Press that there was no storm in the area at the time of the parade.
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