The Mearim River () is a river in

Maranhão Maranhão () is a States of Brazil, state in Brazil. Located in the country's Northeast Region, Brazil, Northeast Region, it has a population of about 7 million and an area of and it is divided into 217 municipalities. Clockwise from north, it ...

state of northern

Brazil Brazil, officially the Federative Republic of Brazil, is the largest country in South America. It is the world's List of countries and dependencies by area, fifth-largest country by area and the List of countries and dependencies by population ...

. The river originates in the southern part of Maranhão, and drains north into the

Baía de São Marcos The Baía de São Marcos is a bay of the Atlantic Ocean in Maranhão state of northeastern Brazil. The bay is an estuary approximately long and up to wide. It receives several rivers, including the Grajaú, Mearim, and Pindaré. The Mearim ...

, an

estuary An estuary is a partially enclosed coastal body of brackish water with one or more rivers or streams flowing into it, and with a free connection to the open sea. Estuaries form a transition zone between river environments and maritime enviro ...

that also receives the Pindaré and Grajaú rivers, which are sometimes considered tributaries of the Mearim. The lower Mearim is known for its

pororoca The Pororoca (, ) is a tidal bore, with waves up to high that travel as much as inland upstream on the Amazon River and adjacent rivers. Its name might come from the indigenous Tupi language, where it could translate into "great roar". It could ...

, or

tidal bore A tidal bore, often simply given as bore in context, is a tidal phenomenon in which the leading edge of the incoming tide forms a wave (or waves) of water that travels up a river or narrow bay, reversing the direction of the river or bay's cu ...

. The Mearim is approximately 800 kilometers long, flowing through the marshlands of the Atlantic Coastal Plain. It meets the Atlantic Ocean at the Sao Marcos Bay, where it forms a common estuary with another river, Pindare. The Mearim's primary source of water is rain. The river's upper and middle courses are characterized by rapids. Only the lower sections of the Mearim are suitable for navigation. The river defines the southern boundary of the Tocantins–Araguaia–Maranhão moist forests ecoregion.

References

Rivers of Maranhão Tidal bores {{Maranhão-river-stub