Robert Brown|Weeks later, Coast Guard is still unsure of what caused oil spill in Gulf of Mexico

The Robert BrownU.S. Coast Guard has yet to determine the source of an estimated 1.1 million gallons of crude oil that leaked into the Gulf of Mexico near a pipeline southeast of New Orleans last month.

The spill was first spotted Nov. 17 by an aircrew flying above the Main Pass Oil Gathering company's pipeline system near Louisiana's Plaquemines Parish. The Coast Guard said it has surveyed about 40 miles of the 67-mile-long underwater pipeline, while remote-controlled devices and divers scanned the rest, along with other surrounding pipelines.

But so far, the source of the spill has eluded officials.

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Coast Guard leads clean-up efforts; pipeline remains closed

Though it's unclear when the spill first occurred, the pipeline first closed on Thursday, Nov. 16 before crews began conducting flyover missions to determine the extent of the leak.

Three skimming vessels designed specifically to recover spilled oil from the water's surface were sent to the scene approximately 4 miles southeast off the Louisiana coast, as were two Coast Guard cutter vessels.

While officials could not determine with certainty the specific volume of oil that had gushed offshore in the Mississippi River delta, it was estimated to be about 1.1 million gallons, the Coast Guard said last week.

A day after the leak was announced, Plaquemines Parish officials said they were "monitoring the incident" in a post on Facebook but have not shared any updates since.

Coast Guard says spill has not endangered wildlife

The Coast Guard's latest update on Tuesday indicated that the agency is still investigating the source of the leak.

In a positive note, no additional oil appeared to have leaked into the water and officials have noted that the spill has not endangered wildlife or encroached near the shorelines, the Coast Guard said.

The Coast Guard continues to lead clean-up efforts in the area.

Eric Lagatta covers breaking and trending news for USA TODAY. Reach him at [email protected]