Bay of São Marcos Bay is one of the Brazilian state of Maranhao.The bay is an estuary approximately 100 km long. It receives several rivers including the Grajaú Mearim and Pindaré. The Mearim is known for its tidal bore.
It is essential for sea transport between the island of São Luís do Maranhão and west, and on its banks are major ports such as Port Itaqui, Ponta da Madeira and Cujupe.
