Mar Chiquita, Coastal lagoon in Buenos Aires Province, Argentina

Mar Chiquita is a coastal lagoon in Buenos Aires Province that stays connected to the Atlantic through a narrow tidal channel. The water surface shifts constantly with tides and currents, while sandbars and dunes change shape across the seasons.

The lagoon lies 30 km north of Mar del Plata. Between 1968 and 1972 the site served as a suborbital launch base at 37°45' S, 57°25' W, from which eight Arcas sounding rockets, two Orion-1 rockets and one Dragon rocket were fired. UNESCO designated it a Biosphere Reserve in 1995, and Argentina made it a wildlife refuge in 1998, covering 560.3 km2.

The lagoon's name, "Little Sea", comes from its widening into an inland sea behind the dune chain. Six streams feed it, among them the Vivoratá and the Dulce from the Tandilia range, and the mix with Atlantic water through the mouth raises salinity in summer. A small resort of 487 people (2010) sits on the southern shore.

The area works well for birdwatching, especially during migration periods in spring and autumn. Paths along the shoreline stay mostly accessible, though wind conditions and water levels affect daily conditions.

Salinity and water temperature fluctuate with seasons and rainfall, bringing different fish species at different times. Some Antarctic birds follow cold currents this far north and use the lagoon as a temporary stopover.