LOUISIANA (CNN) -- A natural gas leak in the Gulf of Mexico has left a four-mile-wide "rainbow sheen" on the water's surface south of Louisiana, the Coast Guard said Tuesday, but the owner of the well said it expects the leak to be plugged within a day.
Houston, Texas-based Talos Energy said the gas is flowing from a well that it was in the process of abandoning. The leak happened while it was trying to permanently plug the well, located about 74 miles southeast of Port Fourchon, Louisiana.
Talos said it evacuated all five staff members from the platform and shut down the two other working wells there. It notified the Bureau of Safety and Environmental Enforcement and the Coast Guard and began a spill response.
"We expect that the well will be shut in within the next 24 hours," Talos said in a statement Tuesday.
Along with the gas, the well leaked about six barrels of oil, or about 252 gallons, the company said, adding it expects the oil to evaporate quickly.
The Coast Guard and BSEE officials flew over the leak Tuesday and found natural gas still flowing from the well, with a rainbow sheen visible on the surface measuring more than four miles wide by three-quarters of a mile long, the Coast Guard said.
The well is on the sea floor, about 130 feet deep, according to a U.S. congressional source briefed on the incident. There is a concern that the gas leak could have a toxic effect on marine life, even if it is stopped by Wednesday.
"Toxic gases will damage the bodies of fish that come into contact by damaging their gills and causing internal damage," said Jonathan Henderson of the Gulf Restoration Network, an environmental advocacy group in New Orleans. "Marine species in the Gulf are more vulnerable when water temperatures are high and when oxygen concentrations are low like they are now."
Talos said the well is older and in a field developed in the 1970s. By 1998, the well was producing mostly water at a low-flowing pressure, so the company was plugging and abandoning it.
The company said it believes the age of the tubing may have contributed to the leak, though the Coast Guard said the cause is still under investigation.
The Coast Guard said the well is owned by Energy Resource Technology Gulf of Mexico. Talos acquired the company earlier this year.