NEW ORLEANS (AP) — A crude oil spill covered about one-fifth of a remote national wildlife refuge near the mouth of the Mississippi River on Wednesday, and another 120 square miles in the Gulf of Mexico, the Coast Guard said.

No affected birds or animals had been reported, and more than 50 people and 16 vessels were working Wednesday to clean up the spill from a pipeline through the Delta National Wildlife Refuge, Lt. Stephen Nutting said.

Nutting said the slick covered 16 square miles of the refuge, which comprises about 76 square miles of marshland between the Mississippi River and Breton Sound and the Gulf of Mexico. A 12-mile-wide slick stretched 10 miles into the Gulf of Mexico, he said.

Crews put 5,000 feet of containment boom around the slick and were putting out another 2,000 feet of boom around the environmentally sensitive area near Breton Island, Nutting said. He said skimmer boats had sucked up 600 gallons of oil.

A Berry Brothers General Contractors barge dredging for ExxonMobil U.S. Production Co. in the area notified the Coast Guard about 1 a.m. that oil was spilling into a canal about 10 miles southeast of Venice, according to a news release.

About 18,000 gallons of oil spilled before Cypress could close the broken section.

The news release was distributed jointly by the Coast Guard, the state of Louisiana and the pipeline operator, Cypress Pipe Line Co. — a joint venture between BP PLC and Chevron Pipe Line Co.

Nutting would not comment on the cause.

ExxonMobil has offered to help deal with the spill, company spokesman David Eglinton said in an e-mail.