Lake Arenal Regions Costa Rica Central America

"This natural depression caused by local geological faults formerly contained a small lake that emptied into the Arenal River which flowed into the Caribbean via the San Carlos and San Juan Rivers. However, in the 1970's, the Costa Rican Electric Company (I.C.E.) began construction of what is currently the country's largest hydroelectric generating project. -- Richard Garrigues, Gone Birding