East Mount Mottarone separates Lake Maggiore from Lake Orta, while to the west mountains as high as 1300 meters separate the water surface from the Valsesia. It is the most western of the pre-alpine lakes, originated from the southern front of the glacier Simplon. Contrary to what happens with many alpine lakes, which have an outlet to the south, the waters of Lake Orta leaving the lake to the north. Through the city of Omegna creating the stream which flows into the Strona Nigoglia which, in turn, flows into the Toce and then into Lake Maggiore.
At the center of the lake lies the island of San Giulio, of small dimensions, which houses the remains of the saint in the Basilica of the same name.