GREENSBORO—Cleanup efforts continue in Greensboro at a retention pond off Bridford Parkway.

On Wedensday, HAZMAT crews were called to the area after they discovered someone dumped dozens of gallons of a thick oily substance in the pond.

They’re working from sun up to sun down, cleaning up what environmental leaders are calling a huge mess.

"We're thinking it could be almost like a tar, or some type of material that goes on pavement or is used to seal paved roads,” said Peter Schneider with the Greensboro Water Resources Department.

It’s much thicker than motor oil, and much larger than originally thought.

"It's a pretty large quantity,” Schneider said. “Based on the information I've seen, upwards of over 50 gallons of material."

Volunteers with Piedmont Wildlife Rehab. rescued their eighth Canada goose Thursday.

"We have reports of several birds behind the Target store that are oiled,” said volunteer Fran Martti. “We know that there are at least four more birds over here where the team is cleaning up."

Volunteers' goal is to stay around the affected area as long as they need to.

"Dawn isn't going to touch the oil on the birds,” Martti said.

The birds will be sent to Carolina Waterfowl Rescue in Charlotte to get cleaned up.

"Two were really critical,” Martti said.

Investigators say managers from the stores next to the retention pond have stepped up, providing surveillance video that could be key in figuring out who dumped the substance into the pond.

"It was early Wednesday morning that they noticed a small truck with a small tank on the back, that was driving very slowly around the parking lot area where the discharge occurred,” Schneider said.

Investigators have now pinpointed the dump site to an area off Landmark Center Boulevard.

"We're having some video surveillance of the storm sewer system in the underground pipes to see how extensive the discharge is,” Schneider said.

It’s an extensive mess that HAZMAT crews and wildlife rescue leaders expect will take several more days to clean up.

Leaders with the city's water resources department say the spill was contained to the pond, and drinking water isn't affected.