Along the Texas coast, barrier islands have nearly enclosed narrow estuarine lagoons, leaving only small openings to the gulf. Those with major freshwater inflow are subjected to widely varying salinity levels, while several that receive only minimal fresh water are actually hypersaline. On the Pacific Coast, San Francisco Bay is the only estuarine system similar to the large eastern estuaries, both because of its physical makeup and the dense urban and industrial development along its shores. The North-Pacific Region extends from northern California to Alaska and contains some 40,000 miles of tidal coastline. Most coastal rivers here drop quickly from the mountains to the sea and culminate in relatively small estuaries.
Every estuary is unique, yet all estuaries share certain features.
Some are similar enough to be grouped or classified according to their shared characteristics. Others are typical of specific regions. All are greatly affected by geology, climate, and a seemingly endless list of other factors, headed by the ever-swelling human population.