In their sandy and flat soils dominate the open grasslands of colored straw in the lower areas and wire cuttings in the slightly elevated areas. Between these zones there are numerous more or less circular lagoons surrounded by marshes, and in the areas bordering the deep estuary small patches of forest of a few hectares appear. This makes it easy to see in San Alonso typical species of grasslands such as gray foxes, collar and deer pampas, along with others more typical of aquatic environments such as yacarés, deer of the marshes and capybaras, and others of the forests like the carayá monkeys. Next to the estancia's hull is the Paraná lagoon where it is not unusual to see river wolves, jacanas, herons and aningas.
Recently CLT biologists were able to verify the presence of the rare ocelot (a miniature yaguareté) in San Alonso.
In addition to these species, on the island you can see reintroduced species such as the collared peccary and the anteater. To these is added the mysterious aguará-guzú, the largest canid in South America, whose cry can be heard at night.
Apart from the landscape and wildlife, one of the main attractions of San Alonso is the CECY, which houses 5 specimens of yaguareté that have been brought to this island to serve as parents of the specimens that may be born in their large fences for then be released in the Iberá and that the ecosystem can count on its top predator; true symbol of Corrientes and Iberá. Access to the CECY will depend on the work of the people in charge and it can not be guaranteed that the specimens that live in it will be seen, since it is normal for them to take refuge in shady areas on the hottest days.