Willie T. Bell, 41, of Palmetto pleaded no contest to an animal cruelty charge, the Bradenton Herald reported.
Police officer Micah Mathews happened to be passing the river on the Palmetto side of the DeSoto Bridge April 25 and saw the dog's snout just above the water. Bell was nearby, wade fishing and swimming.
"Mr. Bell said he was trying to make the dog stronger," Mathews wrote in his report after asking Bell why he would attach the dog to the dumbbell. "The dog was unable to touch the ground and was not able to move the weight."
Mathews directed Bell to get the dog, a 2-year-old pit bull mix named "Blackie," and bring him to shore. The dog had been swimming in place for about 15 minutes.
"The dog is fine and was unharmed," Kris Weiskopf of Manatee County Animal Services said at the time of the incident. "But I believe had the dog been in the water longer it could have become overworked and overloaded. Just think how long you could tread water over your head?"