Costa Rica's largest dams include The Lake Arenal Dam, Lake Cachi Dam, the Rio Macho Dam, the Pirris Dam, the Reventazón Dam and the proposed El Diquís Hydroelectric Project. The Lake Arenal Dam was built in 1979 as the first dam intended solely for hydroelectric power usage. It is located on Lake Arenal next to the famous Arenal Volcano, one of the major tourist attractions in Costa Rica. At about 33 square miles, Lake Arenal provides enough electricity to power 12% of the country. The Lake Cachi, Rio Macho, and Pirris Dams are all powered by the Rio Reventazón (Reventazón River) and its tributaries.