WOLF LAKE – Wild swans found dead last winter along a lake that straddles the Indiana-Illinois border succumbed to infections caused by parasitic worms, the Indiana Department of Natural Resources reported.
The mute swans were found dead along with Canada geese in late February and early March along Wolf Lake, which abuts both Hammond and Chicago’s southeast side.
In early March, a fisherman spotted a dead goose, and later found dozens more. More than 30 dead waterfowl were found in the canal of Wolf Lake on the Indiana side.
The Indiana Department of Natural Resources said that testing by the U.S. Geological Survey’s National Wildlife Health Center in Madison, Wisconsin, found that the swans had fatal infections of parasitic flatworms.
Snails consumed by swans and other waterfowl serve as an intermediate host for that parasite, which causes infected birds to appear weak or unable to fly.
According to DNR officials, intestinal parasite can kill many species of waterfowl, including swans, diving ducks and coots.
However, the agency said researchers could not determine what killed Canada geese that were collected from the same area along Wolf Lake last winter during a cold snap. Those geese tested negative for bacterial and viral infection, lead poisoning, heavy metals and other toxins and ailments.
Lead testing also was performed on the swans, and those results were within the range of non-toxic background levels, DNR said.
All of the dead birds tested negative for avian influenza.
After the dead waterfowl were found last winter, authorities urged the public to avoid Wolf Lake while they investigated the birds’ deaths.