The US Coast Guard on Monday said it was investigating almost 350 reports of oil spills in and along the US Gulf of Mexico after Hurricane Ida.
Ida's 240kph winds wreaked havoc on offshore oil production platforms and onshore oil and gas processing plants.
About 88 per cent of the region's offshore oil production remains shut and more than 100 platforms unoccupied after the storm made landfall on August 29.
The Coast Guard has been flying over the coast of Louisiana looking for spills. It is providing information to federal, state and local authorities responsible for cleaning the sites.
Flights on Sunday found evidence of a new leak from an offshore well and reported that another, responsible for a kilometres-long streak of oil, was contained.
A third report of oil near a drilling platform could not be confirmed, the Coast Guard said.
Offshore oil producer Talos Energy, which hired divers and a clean-up crew to respond to an oil spill in Bay Marchand, said old pipelines damaged during the storm were apparently responsible.
The source of the Bay Marchand leak remains unknown, said Coast Guard spokesman Lt John Edwards.
A Coast Guard-led team "will be looking at all potential sources in order to ensure any future risk is mitigated", Lt Edwards said.
The spill off the coast of Port Fourchon, Louisiana, had decreased substantially since it was first discovered last week, Talos said.
The company is not the owner of the pipelines and had stopped production in the area four years ago, spokesman Brian Grove said.
An offshore well belonging to S2 Energy was discharging oil about 8km away from the Bay Marchand site, the Coast Guard said.
The company told authorities it secured the wellhead and it was no longer leaking.
The Louisiana Department of Environmental Quality said it was working with the Coast Guard and the US Environmental Protection Agency to require companies responsible for spills to stop production and clean up the mess.
"If necessary USCG and/or the EPA can open federal funding streams to cover mitigation costs," the department said.
The environmental agency said: "EPA has received 39 reports relative to the hurricane in our area of responsibility and has been evaluating those reports and following up with responsible parties to ensure they are being addressed."