Immediately, the effects of the Hoover Dike were seen. An extended drought occurred in the 1930s; with the wall preventing water from leaving Lake Okeechobee and canals and ditches removing other water, the Everglades became parched. Peat turned to dust. Salt ocean water intruded into Miami's wells; when the city brought in an expert to explain why, he discovered that the water in the Everglades was the area's groundwater—here, it appeared on the surface. In 1939, a million acres (4,000 km2) of Everglades burned, and the black clouds of peat and sawgrass fires hung over Miami. Scientists who took soil samples before draining did not take into account that the organic composition of peat and muck in the Everglades make it prone to soil subsidence when it becomes dry. Naturally occurring bacteria in Everglades peat and muck assist with the process of decomposition under water, which is generally very slow, partially due to the low levels of dissolved oxygen. When water levels became so low that peat and muck were at the surface, the bacteria interacted with much higher levels of oxygen in the air, rapidly breaking down the soil. In some places, homes had to be moved to stilts and of soil was lost.