One of the most interesting natural attractions is known as Manchón-Guamuchal, a swampland fed by the Ocosito hydrographic system, including the Pacific slope coastline of San Marcos and Retalhuleu. There are different aquatic systems in this zone, including beaches with dune vegetation, thorn bushes, dry forest, sweet water lagoons with emerging vegetation composed mainly of grassy outgrowth and flooded forests. This is Guatemala´s second most dense mangrove forest. Its eco-biological aspects make it important for conservation in order to maintain a balance between the land and sea ecosystem. The flooded plains and coastal lagoons provide food and refuge to large bird populations (CECON, 1995).
Due to its enormous natural resources and biological importance, Manchón-Guamuchal has been declared Special Protected Area (Protected Areas Law, Decree 4-89, and Guatemalan Congress). In as ecosystem, within Retalhuleu´s jurisdiction, there is a finca known as La Chorrera, currently registered Manchón-Guamuchal Private Natural Reserve. In addition to its natural wealth, it is also a Ramsar site which is the title given to all those swamplands recognized internationally for their importance with respect to environmental conservation. These features make this reserve one of the department´s most important ecotourism stops for local and foreign tourists and anyone interested in scientific or specialized interest such as bird watching. Between resident and migratory species, there have been some 425 sightings of birds in this area.