The Tana is one of the largest rivers in Norway and the most important for the Atlantic salmon Salmo salar. The Site is part of its estuary, one of the few unspoilt river estuaries of this size in Europe, which is shallow and partly brackish, with huge underwater deposits of gravel and some sandy islands. It is particularly important for the goosander Mergus merganser, with 21,000 individuals recorded in October 2010. The Site is also important for the nationally threatened harbour seal Phoca vitulina; the sand banks are the only place in Norway where the female seals give birth. The River Tana plays a significant role in flood protection and sediment transport and is extremely important for the local Sami culture, both as a traditional means of transport and as a source of salmon. Possible threats include the introduction of invasive species through the unloading of ballast water, potential oil spills and plans for the development of a new quarry on the western side of the Site.