Comprising a large part of the provinces of Loreto, Requena, Ucayali, and Alto Amazonas, it has an area of 2’080.000 hectares making it the largest in the country and in South America. It is also known as the most extensive area of protected floodable forest (vareza) in the Amazon Rainforest. It is bordered by two large rivers: the Marañon in the north and the Ucayali – Puinahua Canal to the south.
Inside the reserve, there are three river basins: the Pacaya River basin, the Samiria River basin, and the Yanayacu-Pucate River basin. There are also numerous lakes, gorges, canals, and oxbows. It has an annual monthly temperature between 20ºC (68ºF) and 33ºC (91ºF) and an annual rain fall of 2000 to 3000 millimeters, which allows for its huge biodiversity: 449 bird species, 102 mammal species (among them the pink dolphin), 69 species of reptiles, 58 species of amphibians, 256 fish species, and 1024 species of wild and cultivated plants. The reserve is a refuge for different endangered species like the charapa turtle (Podocnemis expansa), the spider monkey (Ateles sp.), the giant river otter (Pteronura brasiliensis), the red macaw (Ara macao), cedar trees (Cederla odorata), and others.
Furthermore, there are diverse protection and natural resource management projects like the one aimed at repopulating the taricaya and the charapa river with turtles in the artificial beaches of the reserve. It is truly amazing to watch the final stage of the process, the freeing of the newborns into the rivers, gorges, and lakes of the reserve. The level of involvment of the local population is remarkable. On the edges of Pacaya-Samiria on the banks of the Marañon and Ucayali Rivers, more than 42.000 people live grouped in ninety-four communities and another 50.000 inhabit the 109 villages in the buffer zone. Almost all of them make a living from fishing, farming, or hunting and wild fruit and greens picking.