Estuaries are a special end member of lagoons. They are river mouths that have been drowned by relative sea level rise and contain a mix of fresh and salt water. Both marine and fluvial processes influence them. With long term global sea level rise, many river mouths were inundated with sea water and became estuaries which are very important ecological sites. We had more than geologically typical until we started filling them in.
Tidal range is very important for estuaries.
If the tidal range is low, there is a stable shore line and little mixing of fresh and salt water. Most of the estuary is fresh water, like the Everglades. If the tidal range is high, the ebb and flood of the tide feeds way into the river mouths and tidal channels and mud flats develop. Copywritten 2001 by Dawn Y. Sumner. They may not be published, sold, or redistributed without my written permission.