Laguna de Manialtepec, Coastal lagoon near Puerto Escondido, Mexico

Laguna de Manialtepec is a 15 km long coastal lagoon about 18 km west of Puerto Escondido, Oaxaca. Red mangroves (Rhizophora mangle) and white mangroves (Laguncularia racemosa) line its banks and reach up to 15 meters in height in places. Its water mixes salt, fresh and thermal spring water, giving it a reddish tint from the red mangroves and red algae.

The lagoon's name comes from Nahuatl manial ('spring') and tepec ('hill'), meaning 'hill where water is born', referring to the thermal spring that feeds it. Fishing and ecotourism are now its two main economic activities, with mojarra and robalo caught and boat tours focused on birdwatching and bioluminescence.

The name comes from Nahuatl: manial, "spring," and tepec, "hill," giving "water that is born from the hill," after the thermal spring that feeds the lagoon. Fishing and ecotourism are the two main activities; mojarra and robalo are the catch, and boats leave from the dock at San José Manialtepec.

The lagoon lies 18 km west of Puerto Escondido along Federal Highway 200, toward Pinotepa Nacional; by water it can be reached by boat from Puerto Escondido. Most visitors explore it by boat or kayak launched near the docks of San José Manialtepec. In the rainy season, from July to September, the lagoon breaks through to the sea at a spot called Puerto Suelo or El Carnero.

On certain nights the water of the lagoon glows faint blue-green when disturbed by a paddle or a hand passing through it. The effect comes from tiny living organisms called dinoflagellates, which produce light when they move or are touched.