Environmental Protection Agency Narragansett Bay Commission University of Rhode Island Office of Marine Programs

Estuarine Science

Estuaries Classified by Water Circulation

Estuaries may be classified based on the way that layers of water are formed within the estuary. Most estuaries have a range of salinity from salty sea water to nearly fresh water. The saltier ocean waters are more dense. Since the waters flowing into the estuary from land are less salty, they float on top of the sea water when they meet. Some mixing also occurs where the two water masses meet. Physical and environmental factors such as the shape of the basin, tides, river flow, and wind determine how much the water mixes. Estuary classifications based on water circulation include salt wedge estuaries, partially mixed estuaries, well-mixed estuaries, and fjord type estuaries.

Salt Wedge

Partially Mixed

Well Mixed


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Estuaries Classified by Geologic Features
Estuaries Classified by Water Circulation

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