Chesapeake Bay on the East Coast of the United States and Coos Estuary on the West Coast are both coastal plain estuaries. These, and most other coastal plain estuaries in North America, were formed at the end of the last ice age between 10,000-18,000 years ago. As glaciers receded and melted, sea levels rose and inundated low-lying river valleys. Coastal plain estuaries are also called drowned river valleys.
Other examples of coastal plain estuaries include the Hudson River in New York, Narragansett Bay in Rhode Island, the Thames River in England, the Ems River in Germany, the Seine River in France, the Si-Kiang River in Hong Kong, and the Murray River in Australia.
In the animation below, rising waters flood a low-lying river valley, creating a coastal plain estuary.