Federal authorities are investigating a leak from an underwater oil pipeline off the coast of Louisiana that may have released up to 1.1 million gallons of crude oil into the Gulf of Mexico, the U.S. Coast Guard said Monday.

An oil sheen was seen on water around 9 a.m. Thursday and the Third Coast Midstream Pipeline company reported a pipeline leak 10 minutes later, according to the National Oceanic and Atmospheric Administration (NOAA). An overflight at 2 p.m. that day reported a slick that was 3 to 4 miles wide “with dark oil scattered throughout,” the agency said on its website.

The National Transportation Safety Board said on X, formerly known as Twitter, that it sent a four-person team to do a safety investigation and determine the cause of the leak about 19 miles offshore near Plaquemines Parish, southeast of New Orleans.

The 67-mile long pipeline was closed Thursday morning by the Main Pass Oil Gathering company. Several federal, state and local agencies are investigating the source of the leak, with the Coast Guard leading clean-up operations.

"The volume of discharged oil is currently unknown," the Coast Guard said in a news release Monday. "Initial engineering calculations indicate potential volume of crude oil that could have been released from the affected pipeline is 1.1 million gallons."

The Coast Guard added that there have been no reports of injuries or shoreline impacts as of Monday.

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Multiple overflights observed oil sheens

The Coast Guard has activated the National Response Team, which includes 15 federal departments and agencies responsible for coordinating the response to response to oil and hazardous substance pollution incidents, Reuters reported.

Multiple overflights to assess the incident were conducted on over the weekend, according to the Coast Guard.

Overflight teams observed oil sheens on the surface of the water, the Coast Guard said. And remotely operated vehicles were deployed Friday to search for the source of the leak along the pipeline.

Three skimming vessels were also deployed to recover oil on the surface, the Coast Guard added.

"Additional surface observations are ongoing with two Coast Guard cutters on scene and additional overflights," the Coast Guard said.

Third Coast Infrastructure LLC, which owns Main Pass Oil Gathering, declined USA TODAY's request for comment on Monday.

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Latest oil spill affecting U.S. waters

Thousands of oil spills occur in U.S. waters each year but "most are small in size, spilling less than one barrel of oil," according to the NOAA. But since the 1969 oil spill in Santa Barbara, California, the NOAA said there have been at least 44 oil spills — spilling over 420,000 gallons — in U.S. waters.

The area of the Gulf of Mexico has faced several oil spills including the largest and worst oil spill in U.S history — the 2010 Deepwater Horizon well blowout.

On April 20, 2010, the Deepwater Horizon oil rig exploded, killing 11 people and releasing 210 million gallons of crude oil into the Gulf of Mexico for a total of 87 days. Oil slicks from the blowout covered an area estimated at 57,000 square miles.

The Coast Guard also reported last year that since April 2019, one million gallons of oil have been collected in the Gulf of Mexico off Louisiana as a result of the 2004 Taylor Energy oil spill.

The spill is considered to be the nation's longest oil spill, leaking for the past 19 years. It began when Hurricane Ivan caused an underwater mudslide in September 2004 and destroyed an oil production platform about 11 miles from the Louisiana shore.

Contributing: Doyle Rice, USA TODAY; The Associated Press