CHARLOTTE, N.C. -- Five sick and dead ducks were found at Freedom Park on Sunday, but officials say Monday's water and algae tests came back negative. 

Sunday's discovery led the county to issue a warning for people and pets to stay out of the water until the tests were complete. But with the test results in, the exact cause remains a mystery. 

"We brought some of the water back to our lab and checked it for algae, to see if there were any toxins present, and there were none," said Storm Water Service's Rusty Rozzelle. "And none of the conditions in the water would've caused the ducks to die."

The county says there are a number of potential reasons why the ducks got sick, including eating the wrong food. 

"Well, I think maybe some people feed them the wrong stuff and the water is pretty dirty in that lake," said Ed Echeverria. 

"There's a big billboard that talks about why not to feed the ducks," said walker Antoinette Thorton. 

"They could've contracted a disease, a virus of some sort," Rozzelle said. "That's happened in the past."

County officials have now lifted the ban after the tests came back negative. Storm Water Services say they don't have any plans to do further testing unless more sick ducks are found. 

"Whatever it is, we think it's very isolated," Rozzelle explained. "Only a few ducks were affected."

Volunteers took the deceased ducks to Carolina WaterFowl Rescue for testing and evaluation.

Anyone who finds a dead or ill duck is asked to contact Carolina Waterfowl Rescue at 704-668-9486.