Footage of the gator was captured by Christina Roach who says she was visiting the beach with her family at the time.
"After an hour or so of swimming, a man came running over yelling to get out of the water" and pointed to the alligator, said Roach.
"I immediately yelled for our kids to get out of the water," she said. "We also called the non-emergency line as well to make sure someone was at least notified."
Erie Port Authority Executive Director Julie Slomski told local media they were taking the matter "very seriously."
"We're really asking the public, if you've seen something, please reach out to us. If someone knows of someone that may have released this gator into the waters, we'd love to talk to that individual," Slomski said.
Warning signs were placed in the area and the Erie Port Authority was speaking to a trapper about capturing the alligator, Erie News Now reported.