Another group of scientists is raising doubts the governments claims regarding the BP oil spill. According to a Bloomberg News report, scientists from the Woods Hole Oceanographic Institution say they have discovered a 22 mile plume of degrading crude oil deep in the Gulf of Mexico. That’s about the size of Manhattan.

According to government estimates, 4.9 million barrels of oil escaped from the well between the April 20 explosion aboard the Deepwater Horizon oil rig and the deployment of a containment cap that finally stopped the flow on July 15. Earlier this month, a scientific team led by the National Oceanic and Atmospheric Administration released a report purporting that most of the oil had been captured, burned off, evaporated or broken down in the Gulf.

According to Bloomberg, the team detected the subsurface layer of oil in late May and followed up with 10-days of sampling from June 19 to June 28, using an underwater vehicle and a device lowered by cable to collect the samples. It contains toxic chemicals like benzene, toluene and ethylbenzene, and will likely remain in the ocean for months, Bloomberg said. It could also travel a great distance.

The scientists haven’t been able to track the plume since June, when they were interrupted by Hurricane Alex, Bloomberg said, so it is not known what state it is in now.

In other news, BP now says the blown Gulf of Mexico well won’t be completely killed until September. BP engineers are conducting a series of tests in preparation for a procedure called a bottom kill to ensure the well can withstand the pressure from the operation. There is concern that 1,000 barrels of oil trapped in the blown well may leak out when the bottom kill is attempted, and BP and the Obama administration haven’t decided yet how to complete a relief well that will be used to inject mud and cement into the bottom of the well. The company said the relief has about 50 feet to go before it’s done.

No oil has leaked from the well since it was capped with a static kill procedure last month. But the bottom kill is needed to make sure the well stays sealed.