Olona

For the Hawaiian plant of the same name, see Touchardia latifolia.

Olona
Origin	Principal source at Fornaci della Riana at 548 m (Rasa di Varese). Other springs are at Monte Martica (937 m), Passo Varrò (760 m), Alpe Ravetta (618 m), Pian Waldes (720 m) and Miniera Valvassera (450 m)
Mouth	Po river.
Basin countries	Italy
Length	131 km
Source elevation	548 m
Avg. discharge	14 m²/s
Basin area	1038 km²

The Olona is a 131 km long Italian river, which runs through the provinces of Varese, Milan and Pavia.

The Olona river in Nerviano

The Olona has more than one source; in fact it has six main springs. Three springs are located in the Rasa Valley, just above Varese, whereas other three springs pour water down from the southern side of pleasant Valganna - since 1877 these still clean and fresh mountain waters were historically used, and still are, to make beer in a renowned local brewery, Poretti, now run by Carlsberg.

The Olona river passes through the deep Olona Valley, cut in the poruous soils of the upper Po Valley, eventually flowing in the plain after Legnano. It is in the Olona valley part that the river gets much of the industrial pollution which has made it a byname for venomous waters for decades. Only in recent years attempts to restore the river's ecology have proven at least partially successful. After Legnano, the Olona river flows in the plain until Milan, usually contained in narrow artificial banks. New expansion basins are being constructed to prevent floodings, which are rare but can be devastating under conditions of sudden intense rain in the upper river flow.

The river passes through Milan mostly under road level. In Milan the Olona cedes part of its water to the Lambro meridionale, to later continue southward in the Bassa (lower Lombard Po Valley). The Olona flows into the Po near San Zenone al Po.

The Olona river counts 39 tributaries. The principal tributaries are the torrents Vellone, Bevera Varesino, Lanza (or Gaggiolo), Bozzente, Lura, Merlata and Mussa.

References

This article incorporates information from this version of the equivalent article on the Italian Wikipedia.