Oil storage tanks ruptured by Hurricane Katrina may have dumped as much as 3.7m gallons of crude oil into the lower Mississippi river and surrounding wetlands.

Officials estimate the spillage at roughly a third of the volume of the huge spill when the tanker Exxon Valdez ran aground off Alaska in 1989. Last night experts said they could not yet assess the short-term effects of the spills but were hopeful there would be few long-term effects. Some of the oil is expected to find its way into the Gulf of Mexico.