A dam is a barrier across flowing water that obstructs, directs or slows down the flow, often creating a reservoir, lake or impoundments. Most dams have a section called a spillway or weir over which, or through which, water flows, either intermittently or continuously, and some have hydroelectric power generation systems installed.Dams are considered "installations containing dangerous forces" under International Humanitarian Law due to the massive impact of a possible destruction on the civilian population and the environment. Dam failures are comparatively rare, but can cause immense damage and loss of life when they occur. In 1975 the failure of the Banqiao Reservoir Dam and other dams in Henan Province, China caused more casualties than any other dam failure in history. The disaster killed an estimated 171,000 people and 11 million people lost their homes. In 2012 a dam in northern state of Rio de Janeiro, Brazil failed forcing thousands of people from homes. The water broke through the dam protecting the town of Campos de Goytacazes. Officials described the situation as race against time to evacuate people before the area becomes flooded. Since this incident, the Brazil government has step up early warning systems to ensure people evacuate before floods strike.