Lillsjön (Swedish: The Small Lake) is a small lake in the western suburb Bromma in Stockholm, Sweden. It is one of four lakes in the western suburbs, the other being: Kyrksjön, Judarn, and Råcksta Träsk. Located in the small park Lillsjöparken and surrounded by heavily trafficked artery roads on all sides, it is rich in nutrients with high levels of metals in the sediments.