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Lake Maracaibo (Spanish: Lago de Maracaibo) is a brackish lake located in northwestern Venezuela, between the states of Zulia, Trujillo, and Mérida. Hydrologically, it is a semi-enclosed bay off the coast of the Gulf of Venezuela. Lake Maracaibo is commonly considered a lake, though due to its current geological characteristics, it should not be considered as such. With a surface area of 13,512 km (5,217 sq mi), it is the largest lake in South America and one of the oldest on Earth, having formed disputably as a lake 36 million years ago in the Andes Mountains.

The lake is connected to the Gulf of Venezuela to the north by a narrow spit. It is fed by numerous rivers, the biggest being the Catatumbo River. The fault in the northern section has collapsed and is rich in oil and gas resources. It is Venezuela's main oil producing area and an important fishing and agricultural producing area. Eutrophication caused by oil pollution is a major environmental problem facing the lagoon. The area around the lagoon is inhabited by a quarter of the country's population and is also the place with the most frequent lightning on earth. The famous Catatumbo lightning can illuminate nighttime navigation.