Editing Marine biology (section)

===Estuaries===
[[File:Urdaibai, Bizkaia, Euskal Herria.jpg|thumb|left|Estuaries have shifting flows of sea water and fresh water.]]

[[Estuaries]] are also near shore and influenced by the [[tides]]. An estuary is a partially enclosed coastal body of water with one or more rivers or streams flowing into it and with a free connection to the open sea.<ref name="james">{{cite book |last=Pritchard |first=D. W. |year=1967 |chapter= What is an estuary: physical viewpoint |pages=3–5 |editor-first=G. H. |editor-last=Lauf |title= Estuaries |series=A.A.A.S. Publ. |volume=83 |location=Washington, DC }}</ref> Estuaries form a transition zone between freshwater river environments and saltwater maritime environments. They are subject both to marine influences—such as tides, waves, and the influx of saline water—and to riverine influences—such as flows of fresh water and sediment. The shifting flows of both sea water and fresh water provide high levels of nutrients both in the water column and in sediment, making estuaries among the most productive natural habitats in the world.<ref name="McLusky">{{cite book |last1=McLusky |first1=D. S. |last2=Elliott |first2=M. |year=2004 |title=The Estuarine Ecosystem: Ecology, Threats and Management |location=New York |publisher=Oxford University Press |isbn=978-0-19-852508-0 }}</ref>{{clear left}}