The Isonzo Rivermouth Nature Reserve covers an area of approximately 2400 hectares (c.6000 acres) situated along the final 15 km (10 miles) of the course of the river.
The Reserve offers the possibility to study a wide range of interesting animals, often belonging to species which are rare or unusual elsewhere. After the establishment of the protected area, through the action of both passive management and active conservation the most obvious effect in the increase in biodiversity has been on the birdlife. This is constantly monitored, and thus far more than 300 species of birds have been recorded. As far as the mammals are concerned, thanks to the peacefulness of the place and its closeness to the limestone Karst, one can find a good number of species including the roe deer, the fox, the badger, the wild boar, as well as numerous species of rodents, bats and insectivores: amphibians are obviously abundant given the nature of the site.
The reserve holds a wide range of plant species typical of freshwater, brackish and saltwater environments. Some carmargue horses have been brought to the site, a breed which, for its physical characteristics (large hooves and fairly small size) is especially adapted to life in wetlands.