The reserve covers two distinct river stretches: the first upstream of the town of Predosa, and the second located between the village of Retorto and Casal Cermelli.
Willows and poplars occupy the outer parts of the riverbed and the gently sloping banks of the stream.
Some remaining portions of intact riparian woodland host wildlife such as foxes, badgers, martens, weasels, hares, roe deer, and wild boars originating from the Apennines.
Among the nesting herons (black-crowned night heron and little egret), the grey heron, water rail, tern, and little ringed plover are also present.
In the stream bed, it is still possible to find some golden spined loach, and occasional seekers come to look for them.
This protected area in the Alessandria province was established to safeguard some intact patches of riparian forest and involves two distinct stretches of the flat-flowing Orba stream.
The first section, located upstream of Predosa, is characterized by small oxbow lakes with rich marsh vegetation and tall trees.
The second section, situated further downstream and enclosed within the main embankments, includes floodplain areas with both natural and cultivated lands, within the territory spanning the village of Retorto, Bosco Marengo, and Casal Cermelli.
During spring and summer, along the natural riverbanks, the stream hosts a large group of colorful birds such as the European bee-eater and kingfisher, which nest on the steep slopes by digging their nests into the earth.
The vegetation is varied and diverse: shrubs, willows, and poplars occupy the outer riverbed areas, while the higher and drier zones feature cereal crops interspersed with small woodlands.
More than a thousand years ago, the famous Selva d’Orba forest stretched along the river slopes. Over time, it underwent significant deforestation due to agricultural activities by Cistercian monks and the demand for timber for the shipyards of the Maritime Republic of Genoa.