Comprising approximately 8,000 hectares, this lagoon, located in the department of Rocha, is unique in that its connection with the ocean is via a natural canal, the Valizas stream. It runs for 17 km and exhibits marked meanders, arcs of its primitive bed, with small islands in its tributaries. This creates a landscape of great beauty, with the added feature of the longest yearly connection with the ocean, with strong currents to and from the sea and frequent wind tides.
The lagoon’s main tributaries are the Arroyo Castillos, de Chafalote, de las Piedritas, del Consejo, Cañada de los Olivera and Arroyo Valizas itself.
Another unique feature of this lagoon is the sandy strip around a large portion of its coast, with a natural forest dominated by coronillas (Scutia buxifolia) and ombú (Phytolacca dioica). A significant part of the lagoon coastline is covered by reeds, which on the north coast are several hundred meters wide and form islands in the lagoon. It holds the largest ombú forest in the Rio de la Plata area. Also unusual are the palm groves, significant from the scenic point of view and also due to their singularity.