Baía de São Marcos is a large, productive bay on the coast of Maranhão, Brazil, characterized by its extensive mangrove-lined shorelines, tidal estuaries, and connection to rivers like the Rio Anil. This estuarine environment creates a rich nursery ground and feeding habitat for a variety of saltwater fish species, supporting both commercial and recreational fishing activities. The bay's geography includes open waters, sheltered inlets, and complex mangrove creek systems, offering diverse angling opportunities from boat and shore.