The Hetch Hetchy Aqueduct is not a river, but rather a crucial water conveyance system in California. This 167-mile long channel stretches across the Central Valley, transporting water from the Hetch Hetchy Reservoir in Yosemite National Park to the San Francisco Bay Area. The system begins at the O'Shaughnessy Dam on the Tuolumne River, which created the Hetch Hetchy Reservoir in 1923. This reservoir, approximately 8 miles long, sits in the northwestern corner of Yosemite National Park, occupying what was once the glacial Hetch Hetchy Valley. From here, water flows through Mountain Tunnels and the Moccasin Powerhouses before entering the aqueduct proper.

While the aqueduct itself is not a paddling destination, the Hetch Hetchy Reservoir offers stunning vistas of the surrounding landscape, including views of Tueeulala and Wapama Falls. However, it's important to note that currently, all water activities including swimming, boating, and paddling are prohibited in the reservoir to maintain the purity of San Francisco's drinking water supply. Access to the Hetch Hetchy area is via a road that's open only during daylight hours. The reservoir is located about 38 miles from Yosemite Valley, or approximately 1 hour and 15 minutes by car. The nearest major access point is the Big Oak Flat Entrance Station on Highway 120.

The flora and fauna around Hetch Hetchy are typical of Yosemite's lower elevations, with a mix of coniferous forests and chaparral. Wildlife includes black bears, mule deer, and various bird species.

Historically, the creation of the Hetch Hetchy Reservoir was highly controversial. The decision to dam the valley in the early 20th century sparked one of America's first major environmental debates, pitting conservationists against urban development advocates. Today, the reservoir and its surrounding area serve as both a critical water source and a unique, if altered, natural landmark within Yosemite National Park.

Visitors to Hetch Hetchy can explore the area on foot, enjoying scenic hiking trails and viewpoints. While water activities are restricted, the area offers opportunities for photography, wildlife viewing, and experiencing a less crowded part of Yosemite. Safety considerations include adhering to park regulations, staying on designated trails, and being aware of wildlife. As with all areas in Yosemite, visitors should practice Leave No Trace principles to help preserve this important ecosystem and water source.