Small lakes in areas of intensive crude oil production may be susceptible to oil pollution arising from accidental spills and leaks, eventually leading to the pollution of bottom sediments. Effective cleaning of aquatic bottom sediments remains a challenge. Flotation is a potentially simple and reliable approach for the cleanup bottom sediments without their excavation from the water body. Full-scale testing of flotation-based technology using the specially designed airlift plant allowed to clear bottom sediments of an unnamed boreal lake (‘the lake) within the Samotlor oil field, North Russia, heavily polluted with crude oil several decades ago. Lake bottom sediments are dominated by peat and unevenly polluted with oil. The average oil content in the lake bottom sediments was 111 g kg−1. During the 1.5 months field test in July–August 2018, the average total oil concentration in the bottom sediments of the lake was reduced to 1.99 g kg−1. Secondary water contamination was minimal; the content of oil hydrocarbons in the water after completion of work did not exceed 0.09 ± 0.04 mg L−1. This study demonstrates that flotation-based technology can be applied for in situ cleaning of oil contaminated lake bottom sediments including those in boreal climate.