Among the natural patrimony of the municipality, Lagoa de Óbidos stands out. It is a wide water mirror, 6 km long, what makes it the biggest lagoon of all country. It finds the ocean through Praia do Bom Sucesso and Foz do Arelho .
Fed by both fresh and salt water, the Lagoa de Óbidos stands out by the fauna that can be found there. Species like snook, eel, flounder, mullet, and also some clams, like razor clam, cockle and mussel are the most relevant fauna in this area. The lagoon also offers excellent conditions for fish spawning and fish farming. Proving it, there are some areas as Poça da Pateira , rich in prawns, and Bom Sucesso , fertile for mussels.
Low depth waters influence the flora. It is remarkable the abundance of macro algae and zostera.
The surrounding vegetation confers a very particular beauty to the lagoon.
The typically calm waters allow the practice of several water sports as rowing, sailing and windsurf and make the lagoon an elected place for fishing.