The Mearim River is a river in Maranhão state of northern Brazil. The river originates in the southern part of Maranhão, and drains north into the Baía de São Marcos, an estuary that also receives the

The Pororoca is a tidal bore, with waves up to 4 m high that travel as much as 800 km inland upstream on the Amazon River and adjacent rivers. It occurs at the mouth of the river where its waters meet