Main Bay is an estuary on the Kenai Peninsula in Prince William Sound, between Port Nellie Juan to the west and Knight Island Passage to the east, about 81 miles (131 km) west of Cordova and 28 miles (45 km) southeast of Whittier, Alaska. The estuary is fed by a watershed of 3,795 acres (1,536 ha), draining mostly from an unnamed lake at 205 feet (62 m) elevation on the northern flank of Eshamy Peak. The descriptive name for the bay was assigned in 1913 by the US Coast and Geodetic Survey. The bay is formed by glacially scoured bedrock of the Orca Group in the Southern Margin or Chugach-Prince William composite terrane, which developed during the late Paleocene to early or middle Eocene (about 60 million to 40 million years ago) and consists of turbiditic sedimentary rocks representing submarine fan deposits. The surrounding rocks are graywacke sandstone, siltstone, mudstone, slate, and some conglomerate. Sedimentary structures—graded bedding, crossbedding, ripple marks, and flute, groove, and load casts—indicate deposition from turbidity currents. The formation is bisected by the Johnstone Bay Fault, aligned with the axis of the lake at the head of the bay. The large ice fields and valley glaciers of the Chugach and Kenai mountains are remnants of a late Pleistocene piedmont glacier that likely extended to the southernmost islands bordering the Gulf of Alaska until about 9,000 years ago. Following deglaciation, Prince William Sound experienced three major glacial advances: the first from about 3,200 to 2,400 years ago, the second around 1,410 years ago, and the third from 650 years ago into the 19th century.

Prince William Sound and its adjacent islands are the traditional territory of the Chugach Sugpiaq, whose ancestors were hunter-gatherers with complex social structures, including ranked societies, shared economies, territorial boundaries, technological innovation, and warfare. Archaeological excavations at Uqciuvit and Palugvik—village sites in the northwestern and southeastern parts of the sound, respectively—point to an earlier prehistoric occupation. Uqciuvit was inhabited from about 3,800 years ago to historic times; Palugvik from approximately 2,200 years ago until at least the early to mid-1700s. Little is known about these pre-Neoglacial people beyond their hunting of sea mammals, use of red ochre, and familiarity with slate grinding. They lived during cool, moist, and sometimes severe weather in a landscape dominated by sedge tundra. Historically, eight geographic groups of Chugach Sugpiaq occupied Prince William Sound. Though sharing the same language and culture, each was politically independent, with its own leader and principal village. Early European explorers noted the relatively small population, a finding corroborated by archaeological surveys. This apparent under-population despite abundant resources may be explained by exposure to raids, seismic activity, or the possibility that Prince William Sound was a marginal habitat despite seasonal salmon abundance.

Pacific salmon have been a vital food source in Alaska for millennia. Commercial exploitation began after the Alaska Purchase in 1867 and grew rapidly with little oversight, leading to unregulated cannery expansion, widespread use of fish traps, overfishing, and population declines that prompted several industry consolidations in the late 19th and early 20th centuries. Stocks fell so low that in 1953 President Dwight Eisenhower declared a federal disaster, yet the decline continued until record lows in 1972. The following year, the Alaska Department of Fish and Game launched a comprehensive fisheries management program, introducing a limited-entry permit system and establishing fish hatcheries. A hatchery for chum salmon was built in Main Bay in 1981. Owned by the state of Alaska, it has been managed and operated by the Prince William Sound Aquaculture Corporation—a private non-profit—on behalf of the Alaska Department of Fish and Game since 1990. Since 1998, the facility has focused solely on rearing sockeye salmon for the Coghill Lake fishery and is currently permitted for 12.4 million sockeye salmon eggs annually. Hatchery associations in Alaska may catch and sell a portion of returning adult salmon for cost recovery. The cost recovery fishery in Main Bay is locally referred to as a gillnet rodeo, see it here. Read more here and here. Explore more of Main Bay and Prince William Sound here: