RÃÂo Grande de Matagalpa (, Awaltara in Miskito, UcumulalÃÂ in Matagalpa) is a river of Nicaragua. Running from its source near Matagalpa to the Caribbean Sea in the northern part of the South Caribbean Autonomous Region it is the second longest river in Nicaragua. It gives it name to the city and municipality of La Cruz de RÃÂo Grande. The TumarÃÂn Dam is being constructed on its lower reaches.