Washington, D.C. ? Authorities searched near the Capitol into the early hours of Saturday morning for possible hazardous materials after more than a dozen ducks were found dead in the Capitol Reflecting Pool.

District of Columbia police and fire department personnel and federal officers tested for chemical, biological and radiological agents after 17 dead ducks were spotted in the pool, D.C. Assistant Police Chief Patrick Burke said. The tests were precautionary because of the proximity to the Capitol, Burke said.

There was no indication of what caused the deaths. The pool is at the east end of the Mall, at the edge of the Capitol lawn.

“It’s a mystery,” D.C. Fire and Emergency Services Department spokesman Alan Etter said. He noted that whatever caused the deaths might have been encountered “at another location.”