Violent storms threaten fight to stop leaking oil
Under thunderous skies here on the Louisiana coast, there's a warning of a new threat to the desperate efforts to fight the leaking oil.
For the past two days the largest clean-up base, at the port of Venice, has been paralysed by a rolling series of electrical storms.
And the head of the US Coast Guard, in a BBC interview, fears worse is to come - including abandoning operations to stem the leak - if hurricanes strike as forecast.
The violent weather is a taste of the potential impact of what is forecast for the coming months - the region's "hurricane season" began on 1 June.
The US Coast Guard, co-ordinating the response to the spill, is drawing up contingency plans to cope with the effects.
Waves could overwhelm the containment booms and high winds could drive the slick further inland, deeper into the wetlands.
Storms may also have a beneficial effect of breaking up the slicks - but no-one can be sure.
The commandant of the Coast Guard, Admiral Thad Allen, told me that hurricanes could disrupt the all-important task of controlling the origin of the spill.
"Coping with this oil spill and solving the leak at the bottom of the ocean is difficult enough by itself but if you add in the threat of hurricanes this becomes a very, very complex challenge," Adm Allen said.
He added: "We need to figure out how to contain the oil, recover it, but knowing that during the hurricane season we may have to pull all our forces off the water."
That would include any vessels involved in collecting oil piped from the well up to the surface - a strategy BP is attempting right now.
"If that were the case the only option would be to have some subsea dispersant at the bottom of the ocean while the ships were gone. But ultimately we would likely have to pull them off," Adm Allen said.
"This is going to be a touch-and-go operation throughout the hurricane season."
A massive challenge
I've seen for myself how the clean-up fleet is vulnerable to the weather.
The risk of lightning striking the hundreds of vessels working out at sea - laying containment booms and soaking up the slicks - kept them confined to the quayside on Wednesday and Thursday this week.
Row after row of boats has been lined up, laden with equipment but unable to venture out into waters heavy with oil.
Until now, the clean-up teams have claimed some success in skimming oil and keeping it back from the coast.
But it's a massive challenge. Here in the Mississippi Delta, the myriad islands and marshes are almost certainly too numerous to protect entirely.
On a boat trip, I saw how many of the reed-beds are now stained with dark oil - the slick reaching into the densest thickets.
In some areas, containment booms have been laid around the marshes to prevent more oil reaching them and to prevent the oil already there from spreading any further.
But the slightest gusts whip up waves that send a lurid sheen from one side of the booms to the other.
The scale of the response is impressive - with thousands mobilised and officials monitoring events in military-style control centres and President Barack Obama promising even more.
But ultimately Nature may have the final say.