Any species which fall into the categories Vulnerable, Endangered or Critically Endangered are considered to be at risk of extinction. Of the nearly 60,000 species assessed so far, this equates to a staggering 20,222 species, from the majestic tiger to the enormous giant clam.
(Photo: Elkhorn Slough NERRS site). An estuary is a partially enclosed body of water, and its surrounding coastal habitats, where saltwater from the ocean mixes with fresh water from rivers or streams. In fresh water the concentration of salts, or salinity, is nearly zero.The salinity of water in the ocean averages about 35 parts per thousand (ppt).ruly, no two estuaries are the same. Yet they are typically classified based on two characteristics: their geology and how saltwater and fresh water mix in them. However, not all estuaries contain brackish waters. There are a small number of ecosystems classified as freshwater estuaries.
An estuary is a partially enclosed body of water where fresh water from streams and rivers mixes with salt water from the ocean. Some river mouths are estuaries. For example, the tidal portion of the Hudson River in New York is an estuary.verview. There are hundreds of thousands of creeks, streams and rivers in the Chesapeake Bay watershed. These tributaries send fresh water into the Bay and offer vital habitat to aquatic plants and animals. These tributaries also provide people with public access points where they can fish, boat and swim.