His body was first spotted floating in the river near New Orleans’ French Quarter by a steamboat captain.
Showers, 45, appeared to have been dead for about two days before he was found. An autopsy is pending to determine the cause of death.
"Michael Showers was a fine actor who contributed his talents to our drama in the warmest and most professional way," said David Simon in a statement from HBO Thursday.
Treme star Wendell Pierce Tweeted Wednesday night: "Rest in Peace to my costar Michael Showers. 'Capt Guidry' on TREME. He will be a lasting part of our New Orleans story and television history."