Estuaries are defined as semi-enclosed bodies of water where fresh water and salt water mix.  Often, their boundaries are difficult to draw but they all have characteristics in common which you will learn more about in this site. 

There are several types of estuaries.  However, in this area, estuaries develop at or near the mouths of rivers.  Barrier islands grow up on the seaward side and provide the chance for the tidal waters from the adjacent saltwater body to mix with the freshwater draining off the land and traveling down the river.  The result is a highly variable mixture where change in terms of salinity, temperature and turbidity is one of the few constants. 

Life thrives here because the barrier islands protect the water body from the wave energy of the sea.   Nutrients flood the water from the land runoff, the shallow waters allow adequate sunlight to penetrate the water column and plants thrive.  The plants are special, extremely hearty varieties that grow at accelerated rates.  This is the energy base for one of the most productive food chains found anywhere on Earth. 

The food chains are unique too.  Instead of having many levels with a great diversity of organisms, they have only a few levels with tremendous numbers of relatively few species. If you have ever seen expanses of mangroves or march grasses or watched flocks of  brown pelicans dive on enormous schools of bay anchovies  you are familiar with the tremendous amount of life in our estuaries.