Swanson River starts at an elevation of 224 feet (68 m) at the outlet of Gene Lake in the Swan Lake district on the Kenai Peninsula and flows generally southwest for 40 miles (64 km), draining a watershed of 162,496 acres (65,760 ha), to Number Three Bay on the southeastern shore of Cook Inlet, about 47 miles (76 km) southwest of Anchorage and 19 miles (31 km) north-northeast of Kenai, Alaska. The watershed is underlain by glacial and lacustrine sediments that were deposited during the Holocene and Late Pleistocene and consist of massive layers of silt and clay, with some sand and pebbly sand, especially near margins of ephemeral glacial and postglacial lakes. Cook Inlet represents a basin lying between two accreted belts of Mesozoic and younger rocks along the southern Alaska margin. Partially filling the basin and exposed on the east and west sides of the basin is a sequence of largely sedimentary rocks deposited during the Paleogene and Neogene periods and are up to 22,966 feet (7,000 m) thick. These rocks are important oil and gas reservoirs for petroleum thought to be sourced from the underlying Jurassic and Triassic rocks.

Richfield Oil Company drilled the first well at Swanson River in July 1957 and struck oil when it tapped the Hemlock Formation. Richfield Oil’s Swanson River Unit No. 1 well produced 900 barrels (143,088 L) of oil per day from a depth of 11,150 feet (3,400 m) to 11,215 feet (3,420 m). The company had leased 71,680 acres (29,008 ha) of the Kenai National Moose Range and more discoveries followed. By June 1962, about 50 wells were producing more than 20,000 barrels of oil per day. This discovery is credited for providing the economic justification for statehood, which was granted in 1959. Today, the federally administered Swanson River unit is still producing oil and natural gas. The Bureau of Land Management currently administers five oil and gas units in the Cook Inlet basin.

Swanson River flows through the Kenai National Wildlife Refuge and in the lower reaches, it passes through the Swanson River Oil Field before turning sharply north. Near its mouth, it flows into Cook Inlet at the Captain Cook State Recreation Area. The river and the many lakes at its headwaters are popular destinations for canoes and kayaks. Two canoe trails are maintained that allow passage through an interconnected system of rivers and lakes. The Swan Lake Route is about 60 miles (97 km) long and includes 30 lakes with portages of up to 0.5 miles (0.80 km). The Swanson River Route is about 46 miles (74 km) long and crosses 40 lakes with portages of up to 1 mile (1.6 km). It is possible to float the Swanson River itself from the outlet at Gene Lake to the Captain Cook State Recreation Area. The Swanson system of lakes and streams supports silver salmon, rainbow trout, and Dolly Varden. Read more here and here. Explore more of Swanson River and Number Three Bay here: