The reserve is located in the estuary of the Gallegos River – Chico River. It has ecological characteristics that favor the settlement of wildlife. The soft, sandy and/or muddy intertidal flats are exposed during low tides and are areas of high biological productivity that provide food for various bird species, especially migratory shorebirds. These environments and the marshes on the upper level of the plains also provide resting areas during their seasonal movements. These wetlands provide optimal conditions for feeding and resting, crucial activities for the survival of migratory birds that must replenish the energy consumed in their extensive and exhausting journeys. Many come from the Northern Hemisphere (Nearctic species), such as the ruddy sandpiper, the sea coot and the white-rumped sandpiper, and join both hemispheres in their seasonal flights, spending the summer in the estuary. Others are exclusive to South America (Neotropical species), including Patagonian species such as the southern oystercatcher and the double-collared plover. It is estimated that the estuary hosts together, between Nearctic and Patagonian shorebirds, more than 20,000 birds per year.