Mar Chiquita is a coastal lagoon located in the southeastern portion of Buenos Aires Province, Argentina, at approximately 37°44′45″S 57°25′39″W. It covers an area of 560.3 square kilometres, making it a substantial body of water with considerable variation in character from one end to the other. The lagoon transitions from conditions resembling open coastal sea near its mouth to freshwater-influenced conditions toward its headlands, giving it an estuarine character throughout much of its extent.

Water depths are notably shallow across most of the lagoon, with a mean depth of less than one metre. The estuarine region typically reaches 1.5 to 2 metres, while the discharge channel at the mouth reaches approximately 3 metres. These shallow conditions are an important consideration for paddlers, as they affect navigation and exposure to wind-driven chop across the broad, open surface.

The lagoon was designated a UNESCO Biosphere Reserve in 1995 and a wildlife refuge by the Argentine government in 1998, reflecting its significant conservation value as a unique estuarine ecosystem. The area supports a variety of animal species, including black drum, which is particularly abundant near the mouth during autumn, spring, and summer. Argentinian silverside and trahira are also present in the broader area.

Motorized boat traffic is present on the lagoon. Vessels operating inside are mostly small craft under 4 metres with outboard engines of around 10 HP, while larger boats of approximately 6 metres with 60 HP engines operate in the inlet area near the mouth. Paddlers should be aware of this motorized traffic, particularly in the deeper central and mouth areas where boat activity is concentrated. A small resort community is located on the southern side of the lagoon.