Date of this Version
The available evidence indicates that Lakes Managua and Nicaragua were broadly connected in the past, when most of the fish species invaded the "Great Nicaraguan Lake". Due to the lowering of the water level (caused perhaps by tectonic movements and/or erosion produced by the Rio San Juan), Lake Managua became separated from Lake Nicaragua in the Tipitapa area. Water movement from Lake Managua is achieved mostly by seepage through a porous dropoff which prevents the exchange of fishes between the lakes. At about the same time, if not earler, Lake Xilml also became separated. After the more or less permanent separation of the great lakes, other fish species, from the Atlantic versant, invaded Lake Nicaragua, probably via the Rio San Juan, but they have been unable to move into Lake Managua because of the barrier in the Tipitapa River. Occasionally, Lake Managua overflows into Lake Nicaragua, allowing movement of fishes in that direction, but migration in the opposite direction has been effectively restricted.