Lake Mergozzo was once part of the Borromean Gulf and Lake Maggiore. Between the 13th and 14th centuries, alluvial deposits carried by the Toce River filled a section of the lake, separating the two basins. Today, the two lakes, divided by a fertile plain, are connected by a narrow canal, the Mergozzo Canal, also known as the Fondotoce Canal.
The main village is, in fact, Mergozzo, characterized by narrow alleyways formed by stone houses built close together. Its central square is dominated by an ancient centuries-old elm tree: according to historical documents, the tree was already standing in the square 400 years ago; now completely hollow, it has been designated a monumental tree of Piedmont.
Mergozzo has been a land of ancient settlements, as demonstrated by the rich collection of the Antiquarium Museum, where materials dating back to prehistory and the Bronze Age are displayed, as well as the ancient tools used for quarrying and working the granite of Montorfano and the marble of Candoglia, the material used to build the Milan Cathedral.

With an average depth of 45 meters and a maximum depth of 73 meters, the lake contains a water volume of 82 million cubic meters. The theoretical water renewal time is six years. The quality of the water has been very good for many years, thanks to the ban on motorboats and to the sewage collection system of the municipality of Mergozzo, with treated waters being discharged into the Toce River.
Due to its particular morphological situation, which results in low wind activity, the waters remain calm and are especially suitable for canoeing and other water sports.