The Site comprises three large marine tidal areas located in the inner part of the Balsfjorden fjord, which at low tide reveal large areas of mud and sand flats. Wet coastal meadows are found between the tidal areas and cultivated land outside the Site boundaries, while gallery forests line the Site in some locations. Several rivers and streams discharge into the fjord through the tidal flats within Kobbevågen and Sørkjosleira. The third area, Grindøysundet, was added in 2017; it contains some small ponds of importance for birdlife. The fjord has high densities of intertidal invertebrates and fish populations which support large numbers of shorebirds and seabirds. Balsfjorden, and Sørkjosleira in particular, is important as one of only two resting sites in northern Norway for large numbers of spring migrant knots (Calidris canutus islandica), which fly directly from early spring staging areas in the United Kingdom and the Wadden Sea. They stay in Balsfjorden for two or three weeks in May and build up substantial fat reserves before apparently flying non-stop to their breeding grounds in Greenland and Arctic Canada. The site is also very important as a staging, moulting and wintering area for a number of other waterfowl species, including swans, divers, grebes, ducks and waders. Some livestock grazing and gravel quarrying is practiced by local people, but the Site enjoys low traffic and little human impact. The birds in the area are annually monitored and research on birds by the Norwegian Institute for Nature Research continues.