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 the place in the water where a tide and a river current meet, like the estuary at New York Harbor, where the Hudson River meets the Atlantic Ocean. Estuary, pronounced ES-choo-air-ee, comes from the Latin word aestuarium, meaning a tidal marsh or opening. The calm waters of an estuary, where the mouth of a river connects with the open sea and fresh water mixes with salty ocean water, makes the perfect home for many species of aquatic plants and animals.