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(CNN) – Highway patrol troopers in Oklahoma fatally shot a man whom they had been trying to get out of high water, authorities said.

The two troopers responded to a stranded motorist call south of Tulsa late Friday and found two men with two vehicles, said Capt. Paul Timmons of the Oklahoma Highway Patrol.

The troopers told the men to come toward them to safer ground out of the high water, Timmons said. But at some point, an altercation broke out.

The troopers fired, killing one of the men, 35-year-old Nehemiah Fischer, according to Timmons. They arrested the other man, Fischer’s older brother, Brandon, who was uninjured.

The shooting is under investigation.

Timmons said Nehemiah Fischer, 35, was armed. But he said it was unclear why the altercation had broken out.

The highway patrol’s practice is to place any patrolman involved in a fatal shooting on administrative leave. Timmons couldn’t confirm whether that had been done yet for the two troopers in this case.

He declined to disclose the troopers’ names.