The Site consists of 13 sub-sites with sheltered intertidal mudflats, salt marshes, permanent shallow marine waters and rocky shores. There are also the two largest river estuaries in the fjord, notably Gaulosenas, one of very few unspoilt large-river estuaries in southern Norway. Both estuaries play an important role in flood regulation. These wetlands support outstanding biodiversity and are of great importance for migratory birds, in particular geese, ducks, waders and wintering seabirds. Nearly the entire Svalbard population of pink-footed goose (Anser brachyrhynchus) uses the Site as a staging area both in spring and autumn. The nutrient-rich freshwater areas and the numerous islets and skerries in the fjord are the most important areas for breeding species such as the horned grebe (Podiceps auritus) and the great crested grebe (Podiceps cristatus). The shallows also comprise important moulting areas for common eiders (Somateria mollissima) and mallards (Anas platyrhynchos) during summer months. Ørin, Gaulosen, Vinnan and Velvangen are important spawning grounds for the local fjord population of Atlantic herring (Clupea herengius). The Atlantic salmon (Salmo salar) and brown trout (Salmo trutta) also use some of the sub-sites as migratory paths. The sites are used quite often by tourists and residents for bathing, fishing, walking and birdwatching. Trondheimsfjorden (including all sub-sites) is one of ten areas in the national monitoring programme for wintering seabirds and waterfowl. In addition voluntary NGO-based monitoring is ongoing with bird counts and ringing activities.