What is "judarn"

Judarn is the name of a small lake in Bromma, a western suburb in Stockholm, Sweden. Surrounded by the forest and nature reserve Judarskogen, it stretches between Åkeshov and Södra Ängby. Three other lakes are found nearby: Kyrksjön, Lillsjön, and Råcksta Träsk. The name is etymologically associated to ljuda, the verb "to sound".