Boulder water quality officials are working to determine how antifreeze -- enough to alarm passersby -- entered Boulder Creek on Wednesday afternoon near Central Park.

Emergency crews were alerted to a green substance in a section of the creek near 13th Street and Arapahoe Avenue shortly after 2:30 p.m., according to police radio scanner traffic.

City water quality officials and the Boulder Fire Department, which routinely handles emergency calls that may involve hazardous materials, responded to the scene, according to city spokeswoman Sarah Huntley.

Responders determined that the substance was antifreeze that had entered the creek through a storm drain nearby, Huntley said. She said it has been determined that the spill was not the result of any city work taking place in the area, but officials are still working to determine how the contamination occurred.

"It will be up to the water quality folks to determine, if they can, who is responsible for the discharge," she said. "And if they can identify somebody, the person could face code violations."

Concerns about contamination of city water as a result of the spill would depend on the amount of antifreeze that made it into the stream, Huntley said, but that does not appear to be an issue with this incident.

"I don't think they were concerned with any sort of health risk, but obviously it is preferable not to have substances like that entering the creek, which is why we have regulations governing it and response protocols," she said.