ADDA (anc. Addua), a river of North Italy. It rises in small lakes of the Fraele glen, and unites with several smaller streams near Bormio, in the Rhaetian Alps. Thence it flows south-west and west through the fertile Valtellina (q.v.) passing Tirano; the Poschiavino joins it at Tirano and the Malero at Sondrio. It falls into the northern end of the Lake of Como. On issuing from the south-east or Lecco arm, it crosses the plain of Lombardy, and, after a course of about 15om., joins the Po 8m. above Cremona. The lower Adda once bounded the territories of Venice and of Milan. At Trezzo, 20M. N.E. of Milan, there is an important hydro-electric power plant.