On November 10–20, 10:13 pm Brasília official time, the 2009 Brazil and Paraguay blackout due to the failure of transmission lines from Itaipu Dam, the world's second-largest hydroelectric dam, affecting over 80 million customers. The failure was caused by a major thunder storm which affected a key transmission line to southeastern Brazil, causing all 20 turbines at the hydroelectric power plant to shut down due to the abrupt fall of power demand. Four of Brazil's most densely populated states entirely lost power (including the states of São Paulo and Rio de Janeiro) with 14 more states being partly affected. The entire country of Paraguay experienced the power failure. It took about seven hours for the system to fully recover. This is regarded as one of the largest blackouts in history, 10 days fully restored.