Its main tributaries are the Ticino, the Maggia, the Toce (by which it receives the outflow of Lake Orta) and the Tresa (which is the sole emissary of Lake Lugano). The rivers Verzasca, Giona, and Cannobino also flow into the lake. Its outlet is the Ticino which, in turn, joins the river Po just south-east of Pavia.
The lake’s jagged banks are surrounded by the Prealps of Piedmont and Lombardy. The western bank is in Piedmont (provinces of Novara and Province of Verbano-Cusio-Ossola) and the eastern in Lombardy (province of Varese), whereas the most northerly section extends thirteen kilometres into Switzerland, where it constitutes the lowest point above sea-level in that entire country.
The climate is mild in both summer and winter, producing Mediterranean vegetation, with beautiful gardens growing rare and exotic plants. Well-known gardens include those of the Isola Madre, Isola Bella and the Isole di Brissago, that of the Villa Taranto in Verbania, and the Alpinia botanical garden above Stresa.