Normally the flow from a well is measured on a rig, but the flow meters on the Deepwater Horizon were destroyed in the explosion on 20 April. Since then, scientists have used several methods to measure the flow. Satellite photos show the extent of the slick on the sea surface.
Combining this data with estimates of the thickness can give an estimate, but it is very uncertain, says Geoffrey Maitland, professor of energy engineering at Imperial College, London. It depends partly on how much oil has reached the surface.
Experts in fluid mechanics are tracking particles coming out of the broken riser and measuring their velocity. They are refining their models of the flow, based on the levels of oil, gas and solid particles coming from the well.
Other estimates are based on the video from the downhole of the well.
A team from the Wood Hole Oceanographic Institution in the US is also using acoustic techniques to measure flow rates.
The birds that arrive badly injured are euthanized. With so many birds coming in and so many more expected, there simply is no time to try to save them.
The sickening, helpless feeling around all this is the birds have to go on making a living with patches of oil moving through the system," he said. "We just don't know how many times can these birds take even a light oiling."
Like most wetlands scientists, Muth cannot say for sure what the impact of oil will bring to this delta.
"Oil is a wild card," he said. "This is an extremely adaptive place. When you throw in a completely unnatural event, like this mass of oil, we just don't know."