Lake Coatepeque (Lago de Coatepeque) is a large crater lake in the east part of the Coatepeque Caldera. It is in Coatepeque municipality, Santa Ana, El Salvador. There are hot springs near the lake margins. At 26 square kilometres (10sqmi), it is one of the largest lakes in El Salvador. In the lake is the island of Teopan, which was a Mayan site of some importance.
Isla Teopán
Lake Coatepeque is also known to change colors from blue to turquoise. According to authorities of the Ministry of Environment and Natural Resources of El Salvador, this is a cyclical phenomenon that occurs from time to time. The color change has happened in 1998, 2006, 2012, 2016, 2017, 2018, and 2019. [3]