Baía de São Marcos is a large coastal bay located in Maranhão, Brazil, forming a common estuary with the Rio Mearim and Rio Pindaré before reaching the Atlantic Ocean. The bay separates the historic city of São Luís from the colonial town of Alcântara, which sits on the opposite shore. This geography creates a significant open-water crossing for paddlers considering a trip between these two points. The bay is subject to oceanic influences, including tides and wind-driven waves. The climate is tropical and lush, with significant rainfall contributing to the river flows that feed the estuary. The water body is part of a major port area, which indicates the presence of substantial commercial boat traffic, including large vessels, particularly near São Luís. The white sandy beaches of Ponta do Farol are located near the bay's edge in São Luís. The overall aesthetic is a mix of urban port scenery, colonial architecture visible from the water, and natural coastal margins. The historic centers of both São Luís and Alcântara, featuring well-preserved colonial buildings with distinctive ceramic tiles, are key cultural sights accessible from the bay. The area has a historical significance tied to the French and Portuguese colonial periods and the region's former wealth from cotton and sugar trades.