Torrente Orba Nature Reserve is located in a predominantly agricultural flatland area, where fields and poplar groves reach as far as the stream banks in some stretches, and natural and agricultural environments alternate. The area is on level ground, with its lowest point at 102 m a.s.l. and its highest at 130 m a.s.l.
Within the reserve the woods are relatively uninterrupted, and composed of different types: in the floodplain there are portions of still intact riverbank wood, with a predominance of willows and poplars; oak and locust woods grow on the drier areas. Narrow pebbly strips run along the stream, while the lower, pebbly terraces above the water present the typical vegetation of dry riverbank grasslands. The Orba stream has national importance because of its flora, and the Reserve is home to several species that are protected by Regional Law No 32/1982, such as Alyssoides utriculata, Leucojum vernum, Echinops sphaerocephalus, Galanthus nivalis, Iberis umbellata, Thalictrum aquilegifolium, and the orchids Anacamptis morio, Cephalanthera longifolia, Neotinea tridentata and Himantoglossum adriaticum. As far as fauna is concerned, birds are the most interesting group, with 211 species reported in the area. Among those that come for breeding there are the corn bunting (Emberiza calandra), the skylark (Alauda arvensis) and, more recently, the quail (Coturnix coturnix), as their presence is linked to the meadows, which have become rare in the flatlands. The breeding colony of Ardeidae in Bosco Marengo is also significant: grey herons (Ardea cinerea), little egrets (Egretta garzetta) and black-crowned night herons (Nycticorax nycticorax) nest there, and they have recently been joined by the Western cattle egret (Bubulcus ibis), which comes every other year. Among mammals, wolves (Canis lupus) have recently returned. Insects include Oxygastra curtisii, a dragonfly protected at European level.
Torrente Orba Nature Reserve is part of the wider Special Area of Conservation and Special Protection Area of the same name (code IT1180002), belonging to the Natura 2000 Network and covering 506 hectares.
