Río Ewan is a river in the Río Grande department of Tierra del Fuego province, Argentina. It originates in the small lake Hantuk, situated in the sierras that mark the northern boundary of the Lago Fagnano basin, and runs approximately 100 kilometers before emptying into the Mar Argentino. The river flows in two separate branches for much of its length, both of which run roughly parallel to Ruta Nacional 3 before converging and turning toward the Atlantic coast. The mouth of the river marks the southern boundary of the Reserva Costa Atlántica, a protected area dedicated to the preservation of seabirds.

The landscape the river passes through is characterized by rolling, shrub-covered hills with lenga beech and ñire woodland, interspersed with broad grassy meadows. The surrounding terrain offers productive grazing land, with sandy soils and high-quality pasture. The region lies within roughly 75 miles of Río Grande, which serves as the primary gateway town for the northern part of Tierra del Fuego.

Río Ewan is primarily known as a brown trout fishery. Brown trout in the broader Tierra del Fuego region can reach upward of 15 pounds, and the Ewan is considered a valuable destination for this fishery. However, the river has experienced repeated incidents of illegal fishing in recent years, which is worth considering when planning a visit. Access to rivers in this part of Tierra del Fuego can be complicated by the fact that many waterways pass through privately owned estancias, and it is advisable to confirm access arrangements in advance, potentially through local tourist offices in Río Grande.

The two named tributaries of the Río Ewan are the Río Ewan Sur and the Río Chapel (also written Capel). Wildlife in the broader Tierra del Fuego river corridor includes guanacos, flamingos, and otters.