Steelhead trout in the context of Fish migration

Trout (pl.: trout) is a generic common name for numerous species of carnivorous freshwater fishes belonging to the genera Oncorhynchus, Salmo, and Salvelinus, all of which are members of the subfamily Salmoninae in the family Salmonidae. The word trout is also used for some similar-shaped but non-salmonid fish, such as the spotted seatrout/speckled trout (Cynoscion nebulosus, which is actually a croaker).

Trout are closely related to salmon and have similar migratory life cycles. Most trout are strictly potamodromous, spending their entire lives exclusively in freshwater lakes, rivers and wetlands and migrating upstream to spawn in the shallow gravel beds of smaller headwater creeks. The hatched fry and juvenile trout, known as alevin and parr, will stay upstream growing for years before migrating down to larger waterbodies as maturing adults. There are some anadromous species of trout, such as the steelhead (a coastal subspecies of rainbow trout) and sea trout (the sea-run subspecies of brown trout), that can spend up to three years of their adult lives at sea before returning to freshwater streams for spawning, in the same fashion as a salmon run. Brook trout and three other extant species of North American trout, despite the names, are actually char (or charr), which are salmonids also closely related to trout and salmon.

A fish wheel, also known as a salmon wheel, is a device situated in rivers to catch fish which looks and operates like a watermill. However, in addition to paddles, a fish wheel is outfitted with wire baskets designed to catch and carry fish from the water and into a nearby holding tank. The current of the river presses against the submerged paddles and rotates the wheel, passing the baskets through the water where they intercept fish that are swimming or drifting. Naturally, a strong current is most effective in spinning the wheel, so fish wheels are typically situated in shallow rivers with brisk currents, close to rapids, or waterfalls. The baskets are built at an outward-facing slant with an open end so the fish slide out of the opening and into the holding tank where they await collection. Yield is increased if fish swimming upstream are channeled toward the wheel by weirs.

Fish wheels were used on the Columbia River in Oregon by large commercial operations in the early twentieth century until they were banned by the U.S. government for their contribution to destroying the salmon population (see below). The wheel's prevalent use in catching salmon, (in particular, salmon species Chinook, chum, coho, sockeye, and pink) and other anadromous species of fish, has given fish wheels their second name as salmon wheels. Although salmon were prioritized by commercial fishers and Indigenous peoples (albeit for different reasons,) other fish such as steelhead trout (Oncorhynchus mykiss irideus), ooligan (Thaleichthys pacificus), and Pacific lamprey (Entosphenus tridentatus) were also considered valuable catch. While the fish wheel is best known for its presence on the northwestern coast of North America, there is debate whether the technology arrived via Asian migrants who had come to labor in the gold fields, by Scottish and Russian migrants, or was a potentially Scandinavian invention sometime during the turn of the twentieth century.

Alameda Creek (Spanish: Arroyo de la Alameda) is a large perennial stream in the San Francisco Bay Area. The creek mainstem runs for 45 miles (72 km) from a lake northeast of Packard Ridge to the eastern shore of San Francisco Bay by way of Niles Canyon and a flood control channel. Along its course, Alameda Creek provides wildlife habitat, water supply, a conduit for flood waters, opportunities for recreation, and a host of aesthetic and environmental values. The creek and three major reservoirs in the watershed are used as water supply by the San Francisco Public Utilities Commission, Alameda County Water District and Zone 7 Water Agency. Within the watershed can be found some of the highest peaks (Mount Isabel and Mount Hamilton) and tallest waterfall (Murietta Falls) in the East Bay, over a dozen regional parks, and notable natural landmarks such as the cascades at Little Yosemite and the wildflower-strewn grasslands and oak savannahs of the Sunol Regional Wilderness.

After an absence of half a century, ocean-run steelhead trout are able to return to Alameda Creek to mingle with remnant rainbow trout populations. Completion of a series of dam removal and fish passage projects, along with improved stream flows for cold-water fish and planned habitat restoration, enable steelhead trout and Chinook salmon to access up to 20 miles (32 km) of spawning and rearing habitat in Alameda Creek and its tributaries. The first juvenile trout migrating downstream from the upper watershed through lower Alameda Creek toward San Francisco Bay was detected and documented in April 2023.