Lost Creek is a tributary of the Koshin River in northwest part of the province of British Columbia, Canada. It flows generally northwest for roughly to join the Koshin River just north of Hatin Lake, and about north of Callison Ranch. Lost Creek's watershed covers , and its mean annual discharge is estimated at . The mouth of Lost Creek is located about north of Telegraph Creek, British Columbia, about west of Dease Lake, British Columbia, and about east of Juneau, Alaska. Lost Creek's watershed's land cover is classified as 46.3% shrubland, 31.5% conifer forest, 12.2% barren, and small amounts of other cover.
Lost Creek is in the traditional territory of the Tlingit Taku River Tlingit First Nation and the Tahltan First Nation, of the Tahltan people.
Lost Creek originates on the north side of the massive Level Mountain shield volcano, near the headwaters of Kaha Creek and Matsatu Creek, about north of Meszah Peak, the highest peak of the Level Mountain Range, a cluster of bare peaks on the summit of Level Mountain. The creek flows north and northwest, first through Level Mountain's high and relatively barren lava plateau, then through rugged forested terrain. In its final Lost Creek enters the Koshin River's floodplain. It empties into the Koshin River in the wetlands along the river north of Hatin Lake. The historic Yukon Telegraph Trail, following the Koshin River, crosses Lost Creek near its mouth.