Lagoa Mundaú is an estuarine lagoon situated west of Maceió, the capital of Alagoas state in northeastern Brazil. The lagoon covers approximately 23–24 square kilometers, stretching roughly 14.22 km in length and 4.22 km at its widest point. It is classified as an estuarine lake type, receiving inflow primarily from the Mundaú River and draining to the Atlantic Ocean. The lagoon is also connected to Manguaba Lagoon via a network of canals that cross a coastal plain, creating numerous small islands throughout the system. Together, Lagoa Mundaú and Manguaba Lagoon form part of the Mundaú-Manguaba Lagoon Estuary Complex, considered one of the most ecologically significant estuarine systems in Brazil.

The lagoon borders three municipalities: Maceió, Santa Luzia do Norte, and Coqueiro Seco. The Pontal da Barra area in Maceió serves as a recognized access point, with a pier used for boat departures into the lagoon system. Organized boat tours operate from this location, navigating through the canal network and stopping at natural features such as the Bica da Pedra complex, which includes natural pools.

The lagoon supports extensive mangrove habitat along its margins, and the waters contain a variety of fish, crabs, shrimp, and shellfish. The canal and island network gives the paddling environment a varied, maze-like character, with mangrove-lined passages and open water sections. Wildlife associated with the estuarine and mangrove ecosystem is present throughout.

Alagoas has a tropical climate. The drier months, generally from August through March, tend to offer more comfortable conditions for outdoor water activities due to reduced rainfall. Paddlers should be aware that motorized boat traffic operates on the lagoon, as commercial tour vessels regularly transit the waterways. A boating accident on the lagoon was recorded in 2023, indicating that vessel traffic and associated hazards are a real consideration. Pollution has been noted as an ongoing concern for the lagoon, and water quality issues should be factored into trip planning. Kayaking and canoeing are water sports activities available in the Maceió area in connection with this lagoon.