page_title: Olona
section_title: The sources
hierarchical_section_title: Olona / Physical geography / The sources
caption_attribution_description: Italiano: Percorsi evidenziati dei fiumi Olona, Olona meridionale, Lambro e Lambro meridionale sovrapposti ad una mappa ottenuta da Open street map.
context_page_description: The Olona is an Italian river belonging to the Po Basin, 71 kilometres long, that runs through the Province of Varese and Metropolitan City of Milan whose course is developed entirely in Lombardy.
  The river born at 548 m s.l.m. in the Fornaci della Riana locality at the Rasa of Varese, at the Sacro Monte di Varese, within the Campo dei Fiori regional park. After crossing the Valle Olona and crossing the Alto Milanese, the Olona reaches Rho where it pours part of its water into the Canale Scolmatore Nord Ovest. After passing Pero, the river enters in Milan, where, at the exit of its underground route, it flows into the Lambro Meridionale, that flows into the Lambro at Sant'Angelo Lodigiano, in the quartier of San Cristoforo ending its course. Along the way, the water system formed by the Olona and the Lambro Meridionale crosses or laps 45 towns receiving the water of 19 tributaries.
  The Olona is known for the waterfalls and caves of Valganna and for having been one of the most polluted rivers in Italy. The valley carved by the river, thanks to the system of water wheels that exploited the driving force originated by the water, was one of the cradles of Italian industrialization.
context_section_description: The principal source of the Olona is in the Fornaci della Riana locality, at the Rasa of Varese, part of the homonymous provincial capital, at the Sacro Monte di Varese, within the Campo dei Fiori regional park. The Fornaci della Riana owe their name to some ancient limestone furnaces that remained active until 1972.
  In addition to the main source, the river also flows from five other small springs, two in Val di Rasa and three in Valganna; these springs give rise to two branches joining downstream from Bregazzana (fraction of Varese).
  The branch that is born to the west, in Val di Rasa, is the most important; the two springs that originate this waterway are located at the Varrò pass (between Monte Legnone and Monte Pizzella) and on Monte Chiusarella.
  The main source, and the one located at the Varrò pass, join upstream from the inhabited area of the Rasa di Varese, while the spring that flows from Monte Chiusarella flows into the Olona downstream. The branch of the Valganna, which is located to the east, was born instead south of Monte Martica.
  The branch of the Rasa is fed by seven small tributaries (more precisely, the torrents Legnone, Grassi, Boccaccia, Brasché, Pissabò, Valle del Forno and Sesnini), while the branch of Valganna is increased by four torrents (the Margorabbia, Valfredda, Valpissavacca and Pedana della Madonna).
  The Valganna branch also gives rise to the Fonteviva lake, dedicated to sport fishing, and to the Valganna waterfalls, which in winter, due to the harsh climate, are often frozen. They are found in the municipality of Induno Olona and are close to the famous and homonymous caves. On the waterfalls, which were artificially created at the beginning of the 20th century to improve water withdrawal, one can admire the phenomenon of travertine surfacing.
caption: Map of Olona, Olona meridionale and Lambro Meridionale
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