In a tweet posted by Houston police, detectives responded to the 1000 block of Commerce Street near San Jacinto.
A security guard patrolling the area said he called 911 about seeing someone floating in the water near Congress and Main.
"All I could see was the head and part of the face," he said. "It was sideways and it was floating away so I couldn't really see the face. The body wasn't real dark, like a body is supposed to be. I couldn't tell what it was."
When firefighters arrived, they pulled the body from the water.
"When I saw [the body], I called 911," said the guard, who told ABC13 the body appeared to be that of a male. "I reported the body floating, and they responded pretty quick."
The identity of the victim has not been released by authorities.