The Back Bay is the colloquial term for the inland delta

River delta

A delta is a landform that is formed at the mouth of a river where that river flows into an ocean, sea, estuary, lake, reservoir, flat arid area, or another river. Deltas are formed from the deposition of the sediment carried by the river as the flow leaves the mouth of the river...

 in Newport Beach, California

Newport Beach, California

Newport Beach, incorporated in 1906, is a city in Orange County, California, south of downtown Santa Ana. The population was 85,186 at the 2010 census.The city's median family income and property values consistently place high in national rankings...

. It connects the Upper Newport Bay

Upper Newport Bay

The Upper Newport Bay is a large coastal wetland in Southern California and a major stopover for birds. Dozens of species, including endangered ones, can be observed here. Upper Newport Bay Nature Preserve and Ecological Reserve represent approximately 1,000 acres of open space...

 with the Newport Harbor

Newport Harbor

- Geography :* Newport Beach, California* Newport Harbor High School, in Newport Beach, Orange County, California* Newport Harbor Light, in Newport, Rhode Island* Newport, Rhode Island* Newport, Pembrokeshire...

. It is a nature reserve home to several species of birds with hiking and biking trails. The bay is recognized for protection by the California Bays and Estuaries Policy

California Bays and Estuaries Policy

The Water Quality Control Policy for the Enclosed Bays and Estuaries of California is published by the California State Water Resources Control Board as guidelines to prevent water quality degradation. The policy is revised as needed.-Geography:...

.
It is a heavily residential area being in the wealthiest portion of both Orange County, California

Orange County, California

Orange County is a county in the U.S. state of California. Its county seat is Santa Ana. As of the 2010 census, its population was 3,010,232, up from 2,846,293 at the 2000 census, making it the third most populous county in California, behind Los Angeles County and San Diego County...

 as well as the city of Newport Beach.