Gastineau Channel is a flooded glacial valley about 15 miles long, separating the mainland from Douglas Island. Juneau sits about halfway up this valley. A few miles north of downtown Juneau, the channel shallows up into a large, fertile intertidal wetlands complex. South of town, it averages about 90-feet deep and runs about 10 miles to the intersection of Stephens Passage and Taku Inlet.
For millions of years, mile-thick ice buried this area, the weight depressing the Earth's crust. At the end of the last ice age, the ice melted and the land began rebounding. The melting of glaciers caused sea levels worldwide to rise about 300 feet, but the land here has risen faster yet. Just 20 miles inland, the Juneau Icefield, a vast network glaciers fed by more than 100 feet of annual snowfall, still holds the land in an ice-age-like grip.
The Mendenhall Wetlands provide year-round wildlife watching opportunities and a number of trails and view points provide access. Above downtown, Mount Juneau rises 3,500 feet, and in the spring mountain goats frequent the grassy slopes. Black bears roam the hills behind town and are a familiar sight in spring and summer.
Gastineau Channel is also a magnet for birds. Spring brings harlequin ducks to the channel, multicolored birds with striking plumage. Great blue herons nest in the trees in and around Juneau, stalking small fish in the shallows. Eagles are abundant.
A variety of sea ducks overwinter in Gastineau Channel, and from the waterfront it's common to see Barrow and common goldeneye, bufflehead, mallards and large rafts of white-winged and surf scoters. Dall's and harbor porpoises also visit these waters, and in the spring killer whales make forays up the channel.
Belted kingfishers perch on pilings and telephone wires over the harbors, watching for small fish. The size of a Steller's jay, with a similar-looking crest, they plunge head first into the water to catch fish. They are fiercely territorial and their rattling call announces their claim to fishing areas.
River otters hunt in the harbors and under the docks downtown, catching sculpin and other small fish and littering the docks with bones and shell fragments from their meals. Their chirping calls and sneezes can be heard echoing among the pilings at night and in the early morning hours. Mink may also be seen scampering between the protective cover of rocks near the waterline. These slinky weasels are about the size of a corn cob, with a lush brown fur coat.
Residents of Alaska's capital city live under the watchful eye of ravens. Unparalleled aviators, these intelligent, acrobatic birds soar in pairs or circle in flocks over town, calling back and forth with expressive coos and gurgles or raucous, badgering cries.
Four miles south of downtown, Sheep Creek flows into Gastineau Channel. At low tide a sandy delta fans into the channel. During July, August and early September, hordes of spawning pink and chum salmon crowd into Sheep Creek, drawing gulls and seals to the area. The bridge at Sheep Creek offers an excellent vantage point to watch the fish build streambed nests (called redds), jockey for mates and lay their eggs. Scores of eagles can be seen resting in nearby trees or feeding on the fish, which die after they spawn. Marbled murrelets and guillemots gather in the salt water just off the delta.
Gastineau Channel is one of the few places where it is possible to see mountain goats from a boat on the water. In spring and throughout the summer, mountain goats may be seen on Mount Juneau and on the long ridge south of Sheep Creek. (Early settlers, mistaking goats for sheep, mis-named this creek). Scan the slopes with binoculars, looking for a scattering of white spots. Closer scrutiny may reveal flocks of goats, their shaggy coats a more yellowish off-white than the lingering snow patches in the area. In June and July, it's even possible to distinguish the smaller kids from the nannies and billies.
Harbor seals are found in Gastineau Channel year-round but are particularly abundant when the salmon are running. Humpback whales are occasionally seen in the channel in summer.
At the south end of Douglas Island, Gastineau Channel opens into a broad expanse of water, the confluence of Stephens Passage and Taku Inlet. Taku Inlet is a deep, glacially carved fjord about 20 miles long. The white flank of the Taku Glacier can be glimpsed at the head of the inlet, where the Taku River meets the sea. This is one of the few glaciers in Southeast Alaska that is actively advancing.
The Taku River flows 55 miles and drains the interior plateaus of British Columbia. It serves as a major migration corridor and as a biological pathway between the coast and the interior. The Taku River supports large runs of Chinook and other salmon species. Throughout much of the summer, commercial fishing boats and recreational anglers can be found plying the waters of the inlet.
The Taku experiences a remarkable annual summer flood that doubles or triples the flow of the river in just two or three days. About 35 miles up the river, the Tulsequah River, a major tributary to the Taku, is blocked by a branch of the Tuslequah Glacier. A lake forms annually behind this ice dam, and in summer the lake fills with meltwater and rainwater. As the lake level rises, it gradually lifts the ice dam, and water begins flowing through a sub-glacial tunnel with increasing volume. At a certain critical point, usually in late July or early August, the dam gives way and a tremendous surge of water is released. (Geologists call this type of surge a "jokulhkaup," an Icelandic word pronounced yo-kul-hape.)
Dead trees and rafts of floating debris are washed down the inlet and into Stephens Passage following these events, creating navigation hazards for small boats and floating perches for opportunistic eagles and gulls.