the salinity of the water body is also a determining factor in the kinds of species found in the water body. organisms in marine ecosystems tolerate salinity, while many freshwater organisms are intolerant of salt. the degree of salinity in an estuary or delta is an important control upon the type of wetland (fresh, intermediate, or brackish), and the associated animal species. dams built upstream may reduce spring flooding, and reduce sediment accretion, and may therefore lead to saltwater intrusion in coastal wetlands.