The Hidden Falls Fish Hatchery is located in the Tongass National Forest on the northeast coast of Baranof Island, at the head of Kasnyku Bay off Chatham Strait, about 22 miles (35 km) south-southeast of Angoon and 21 miles (34 km) northeast of Sitka, Alaska. Hidden Falls, the outlet of Hidden Falls Lake, is situated adjacent to and above the hatchery at an elevation of 210 feet (64 m). The lake measures about 1.3 miles (2 km) long and 0.4 miles (0.6 km) wide, and is fed by several alpine lakes and cirque glaciers. The US Forest Service gave the falls their descriptive name in 1923, as they cannot be seen by boat until reaching the upper end of the small lagoon at the head of Kasnyku Bay. Baranof Island is part of the northern Alexander Archipelago of Southeast Alaska. It was named in 1805 by Captain Yuri Lysianskyi after Alexander A. Baranov, the governor of Russian America and chief administrator of the Russian-American Company. Baranof Island is part of an accretionary block that includes Chichagof Island to the north. It is bounded to the west by the Fairweather Fault, which separates these islands from the volcanic rocks of the Pacific Oceanic Plate. The block is bounded to the east by the Chatham Strait Fault and to the northeast by the Peril Strait Fault. These faults separate the Baranof-Chichagof block from the rocks of Southeast Alaska, which have entirely different stratigraphic sequences and intrusive formations. The northeast coast of Baranof Island is composed of rocks assigned to the Chugach Terrane, consisting of sedimentary and volcanic rocks derived from a subducting oceanic plate. The bedrock surrounding Kasnyku Bay is an igneous intrusive called tonalite, which developed between the Late Paleocene and Oligocene epochs, or 43 to 23 million years ago. This tonalite is mainly represented by the Kasnyku Lake Pluton, which underlies about 64,000 acres (25,900 hectares) of Baranof Island and extends into an additional area of unknown extent beneath Chatham Strait.

In 1978, the State of Alaska constructed a salmon hatchery at Kasnyku Bay, leading to one of Southeast Alaska’s major archaeological discoveries at Hidden Falls. Archaeologists identified 13 distinct cultural layers, revealing three major episodes of human occupation. The oldest layer, Component I, dates back about 9,500 years and featured chipped stone tools, notably small obsidian blades. These microblades were often attached to bone or wood to create cutting edges. Analysis showed the obsidian came from Suemez Island, about 150 miles (240 km) south-southeast, and Mount Edziza, approximately 100 miles (160 km) upstream along the Stikine River. The site was abandoned, possibly due to advancing glaciers, and reoccupied around 4,600 years ago. By this time, Component II tools were made of ground stone and bone, with microblades and most chipped stone tools absent. People in this period relied on a diet of cod and other bottom fish, sea mammals, deer, and birds. They developed methods to catch large volumes of salmon using fish weirs, as indicated by a weir found in Cosmos Cove, about 2 miles (3.2 km) north of Kasnyku Bay. The Hidden Falls site was used as a seasonal camp for approximately 1,400 years. The most recent culture to inhabit the site is known as Component III, dating from about 3,000 to 1,300 years ago. These prehistoric people continued using ground and chipped stone tools but placed greater emphasis on ground bone tools, such as harpoon points for sea mammal hunting. Recovered artifacts reflect a traditional Northwest Coast cultural adaptation, including stone adzes, axes, mauls, and other woodworking tools. This layer also yielded large volumes of shellfish, such as butter clams, littleneck clams, and mussels. Subsistence activities at Hidden Falls focused on resources near the shore, akin to other peoples who occupied the mainland and inner islands to the south. Their maritime adaptation differed from the Aleut, Alutiiq, Haida, and Nuuchanulth who specialized in offshore hunting and fishing, possibly indicating a stronger reliance on terrestrial resources due to the abundance of food at salmon streams, and cedar trees for building canoes and houses.

Salmon enhancement in Alaska began in response to declining salmon populations. From 1945 to 1975, the average annual salmon catch was 83 million fish. However, in the last 15 years of that period, the average catch dropped to 45 million fish per year, and between 1973 and 1975, it was only 23 million annually. In 1969, Alaska received $900 million from North Slope oil and gas leases. The state legislature decided to invest these funds into developing salmon hatcheries to provide long-term employment and economic activity. The goal was to supplement wild salmon stocks with hatchery fish until the total annual catch reached 100 million. In 1971, the Division of Fisheries Rehabilitation, Enhancement and Development (FRED) was established within the Alaska Department of Fish and Game to manage state-owned hatcheries and promote private ones. Today, there are 30 production hatcheries and one research hatchery in Alaska. The Hidden Falls hatchery, operated by the state from 1979 to 1988, was transferred to Northern Southeast Regional Aquaculture Association. It releases 600,000 Chinook smolts, 3 million coho smolts, and 84 million chum salmon fry annually. Returning coho and Chinook are primarily caught by trollers and seiners. From 2001 to 2010, the hatchery produced an average chum salmon return of 1.7 million fish annually, with a record return in 1996 of over 4 million fish. This run has attracted up to 240 seine boats during openings, providing fishermen with significantly greater opportunities early in the season. Initial returns increased substantially due to two major hatchery expansions—one in 1987 and another in 2004. However, in the early 2010’s, survivals at Hidden Falls began to plummet. Brood years 2006 to 2016 averaged just 0.8% survival, and while the decline was most pronounced at Hidden Falls, the trend seemed to be consistent throughout the Northern Southeast Alaska. In 2011, the US Forest Service authorized hatchery interpretative tours for cruise ship passengers. Today, hatchery staff educate visitors about salmon fishery enhancement and aquaculture practices. Read more here and here. Explore more of Hidden Falls Hatchery and Kasnyku Bay here: