Fresh water from land enters the ocean trough rivers, streams and groundwater flowing trough
valleys, these valleys that cannel fresh water from land to salty ocean, which range from extremely
narrow stream cut channels to remarkably broad lagoons behind long barrier islands, are called
estuaries
Estuary systems which vary to reflect the geology of the coasts where they are found
can be broadly categorized as one of two different types
the other category of estuary system encompasses the mountainous coasts with their rugged
topography, such as those ffound along the pacific coasts of north and south America.
A number of types of estuaries are commercially vital; many commercially important estuaries
are the mouths of major river.