Hacksjön is a small lake located east of the former airport at Tullinge, in the municipality Botkyrka in southern Stockholm, Sweden. It forms the westernmost lake of one of the branches of the Tyresån lake system and is located within the Lida-Riksten Open-air Area.
With its isolated location surrounded by moorlands and forests, the lake remains relatively unaffected by human activities, which is mostly limited to precipitation and incoming nutrients from local soil. The lake is used for wireless radio-controlled boats in summers and for ice racing in winters, which have reduced the previously prominent bird life by the lake. Notwithstanding, it is classified as of considerable importance for nature conservation.