Visone (round)

In theList of public waters relative to Province of Alessandria, prepared in 1919 by the Ministry of Public Works, the stream was called torrent Visone di Valpiana e delle Rocche^[3].

The Visone was born about 700 m a.s.l. near Cimaferle, in common of Ponzone, with the name of rio of the Rocche.

Going north, direction that will keep gross unchanged until confluence in the Bormida, changes first in Rio Gambarello and, after receiving from the left the contribution of the Lavandera rio (or Lavanda), definitively becomes the torrent Visone^[4]. The confluence of the Tre Alberghi stream is located just under 300 meters above sea level; the Visone then passes the municipal center of to the west Grognardo, near which it receives the Rio di Verazza from the left, the last significant tributary.

With meandered path, it then enters into common Visone where it is overlaid by both the Asti-Genova Railway and the former SS 456; finally it goes to join the Bormida at 137 meters of altitude^[5].

In the second half of the 19th century, it is attested the presence in its alveo of native gold pagliuzze^[6].

• Rio dei Tre Hotels (8 km long^[7]): it also originates not far from Cimaferle and runs almost parallel to the Visone until its confluence with the latter.
• Rio di Verazza (3.9 km long)^[7]): drains the north-western area of the municipality of Ponzone.

The stream, at least in its upper part, is still quite intact from an environmental point of view and its waters are home to the river shrimp (Austropotamobius pallipes) and various invertebrates indicators of a good environmental state such as plecoptera, ephemeropterans and tricoptera^[4].

In 2001 the macroinvertebrates fauna of this stream and its impact on Bormida have been studied as a possible scientific indicator of the level of resumption of watercourses from previous severe states of pollution^[8]. In the riverbed of the Visone, studies were also conducted to analyze the decomposition process of fish carcasses in a typical Apennine river environment and its role as an energy resource for the river system itself^[9].

From a point of view of the fishing the stream is considered to belong to the category of salmon waters from sources up to Grognardo^[10].