CHICAGO (CBS) — Two months after dozens of dead birds turned up around Wolf Lake in northwest Indiana, officials said testing determined several swans died from a parasitic infection, although it’s still unclear what killed several Canada Geese that also died.

Wolf Lake straddles the Southeast Side of Chicago and Hammond, Indiana. In early March, a fisherman spotted a dead goose, and later found dozens more — over 30 dead waterfowl in the canal of Wolf Lake on the Indiana side.

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Some of the dead birds were ducks and swans, but most were Canada Geese – either lying on the ice or floating lifeless in the water. The mysterious deaths and the possible explanations behind them stirred debate among the people who live in the area.

Hammond is proudly industrial, but there is a fractured trust between some of the industrial plants and residents, some of whom feared the birds might have died from lead poisoning or other heavy metals in the lake.

Wildlife officials conducted extensive testing on the dead birds, and determined the swans had fatal infections of an intestinal parasite known as Sphaeridiotrema globulus, which can kill swans, ducks, and other birds. The swans also were tested for lead poisoning, but results showed lead levels “were within the range of nontoxic background levels,” the Indiana Department of Natural Resources said Monday in a news release.

Officials were unable to determine the cause of death for multiple Canada geese that were also found around Wolf Lake, but were able to rule out bacterial and viral infections, lead poisoning, heavy metal poisoning, salt toxicity, botulism, toxic organic compounds, and avian influenza.

“Wildlife disease investigations can be challenging, especially when multiple factors, including adverse weather conditions, may be involved,” said Julia Lankton, a wildlife pathologist with the United States Geological Survey. “While we could not confirm a cause of mortality for the Canada geese, we are glad that the mortality event seems to have resolved and dead birds are no longer being reported.”

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Officials said deaths in Canada geese near Wolf Lake peaked over a weeklong period in late Feburary, after a stretch of severe cold, and subsided in early March. Swan deaths were not observed until early March.

“The DNR, together with state, federal and private partners, has been monitoring migratory bird populations in the area and mortality seems to have subsided” said Mitch Marcus, fish & wildlife health supervisor for the Indiana DNR Division of Fish & Wildlife.

According to IDNR, the parasite that infected the swans does not pose a risk to humans, pets, or the commercial poultry industry.

“Snails consumed by swans and other waterfowl serve as an intermediate host for the parasite. Infected birds may appear weak or unable to fly and often die. Control measures have not been developed for this parasite, and waterfowl deaths may recur on a regular basis,” IDNR said in a news release.

Anyone who spots dead wildlife in Indiana should report it to IDNR online at

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CBS 2 Chicago Staff