Estuaries are transition zones between saltwater and freshwater ecosystems.
They are located at the mouth of rivers where freshwater meets the saline water of the nearshore. No two estuaries are alike and they are often associated with other coastal ecosystems such as salt marshes, mudflats, beaches and bogs. Tides play a major role in the salinity of the water. With each incoming tide there is an influx of saltwater. When saltwater mixes with freshwater it is termed brackish.