Underwater injection of Corexit into the leak may have created the oil plumes which were discovered below the surface.[138] Because the dispersants were applied at depth, much of the oil never rose to the surface.[147] One plume was 22 mi (35 km) long, more than 1 mi (1,600 m) wide and 650 ft (200 m) deep.[148] In a major study on the plume, experts were most concerned about the slow pace at which the oil was breaking down in the cold, 40 °F (4 °C) water at depths of 3,000 ft (900 m).[149]