With more than a dozen swans found dead around an Indiana lake in recent weeks, authorities said test results showed several carcasses had elevated lead levels.

Local birdwatcher John Madeka, of Hammond, said he has personally discovered at least 18 dead mute swans since October around George Lake.

“I am concerned about these beautiful birds and the people who live next to them in Hammond and Whiting,” he told NBC 5 via email.

Madeka reported the deaths to the Humane Indiana Wildlife, which in turn helped deliver carcasses to the Indiana Department of Natural Resources lab at Purdue University for testing.

In the weeks following, an official with the Department of Natural Resources sent an email to Humane Indiana Wildlife saying the six carcasses tested had “elevated lead levels in the kidneys, some to toxic levels.”

“Results from additional tests, including those for avian influenza, botulism, and other toxicants were negative,” the email, which was then sent to Madeka, read.

The Indiana Department of Environmental Management is investigating the deaths and said the investigation remains ongoing. The department notes that the elevated lead levels "were not found to be the cause of death," however.

"Due to the partial decomposition of the dead Mute Swans, an exact cause of death could not be determined," IDEM said in a statement to NBC 5. "DNR also noted major pathalogical changes were associated with parasitism."

Soil samples from the area earlier this year showed lead contamination in yards in both Hammond and Whiting.

Tests in May found 25 yards with soil lead levels exceeding the federal cleanup standard of 400 parts per million, according to the Environmental Protection Agency. One home's soil tested as high as 2,760 parts per million of lead.

The EPA set aside $1.7 million in taxpayer funds to remove contaminated soil around 20 homes where there were young children or pregnant women. Officials expected to find more contaminated homes as the investigation expanded.

The area is located near the former Federated Metals property, an abandoned smelter that put lead, arsenic and other heavy metals in the air from 1937 to 1983. Some hazardous waste dumped on the property wasn't removed until the mid-2000s.

Other lead-processing companies have operated at the site since Federated Metals closed.

The EPA is also working to clean up lead contamination at a Superfund site in nearby East Chicago, where more than 1,000 low-income residents were forced to evacuate a housing complex last year.

EPA officials told the Northwest Indiana Times the DNR will be taking the lead in investigating the death of swans in the area.