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Alligator Lake, also known as Tadlac Lake, is a freshwater crater lake located in Barangay Tadlac, in the Municipality of Los Baños, Laguna province, Philippines. The lake-filled maar is located along the southern shore of Laguna de Bay, the largest lake in the country, with Alligator Lake protruding out of the shore of the larger lake. If not for its slightly-elevated crater rim, Alligator Lake would be wholly engulfed by Laguna de Bay.[4]

The crater lake is one of the maars of the Laguna Volcanic Field. It is listed as one of the inactive volcanos in the Philippines by the Philippine Institute of Volcanology and Seismology (PHIVOLCS).[5] Lake overturns or carbon dioxide (CO2) eruption from deep within, locally called as langal, normally occurs during the months of December to February. During this period some indigenous fishes of the lake are often observed gasping for air near the lake surface.[6]

Prior to the introduction of aquaculture, Alligator Lake was considered as an oligotrophic lake, having low nutrient content and low algal production, resulting in very clear water with high drinking-water quality

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