Chapala (chäpäˈlä) [key], lake, c.50 mi (80 km) long and 8 mi (12.8 km) wide, W Mexico, in Jalisco and Michoacán states. It is the largest lake in Mexico. Set in a depression on the central plateau, Lake Chapala is fed by the Lerma River, which flows into it from the east, and is drained by the Río Grande de Santiago, which flows out by the northeastern corner. It is a popular scenic resort. Fishing is a local occupation. Since the early 1950s the waters have been receding at an alarming rate and the lake is rapidly becoming choked with water hyacinths; studies have been initiated to determine an effective conservation program.