The U.S. Geological Survey detected changes in groundwater salinity near Florida's Lake Okeechobee following construction of a seepage barrier along the southeastern quarter of the lake. Contractors working for the U.S. Army Corps of Engineers built a cutoff wall to divert the path of water seepage discovered after hurricanes in 2004 and 2005. The flow damaged the 143-mile-long Herbert Hoover Dike, built in the 1930s around the lake for flood control.
Seepage of this sort is responsible for about 20% of dam failures in the U.S., according to the Association of State Dam Safety Officials. In 2007, the Corps listed the dike on a list of dams most at risk and requiring urgent repairs.