The Isorno is an Italian and Swiss river, a tributary of the Melezzo Orientale.
Its source is in Italy near Pioda di Crana where it is called the Onsernone River. It passes through Bagni, a frazione of Craveggia. The official name changes to Isorno upon entering Switzerland, where it flows through Onsernone, Mosogno, Isorno, and finally Intragna where it joins the Melezzo Orientale River. Soon thereafter it flows into Lake Maggiore.
