lake Bolsena

The southernmost end of the lake viewed from the ridge of Montefiascone caldera. Martana is on the left and Bisentino on the right. The straight shore to the far left is Marta. To the left of Martana is the headland of Capodimonte. Lake Bolsena (Italian: Lago di Bolsena) is a lake of volcanic origin in the northern part of the province of Viterbo called Alto Lazio ("Upper Latium") or Tuscia in central Italy. It is the largest volcanic lake in Europe. Roman historic records indicate activity of the Vulsini volcano occurred as recently as 104 BC; it has been dormant since then. The two islands in the southern part of the lake were formed by underwater eruptions following the collapse that created the depression.

The lake is supplied entirely from the aquifer, rainfall and runoff, with one outlet at the southern end. A sewage treatment plant constructed in 1996 filters most of the raw sewage from the major surrounding communities, transported via pipeline to the facility on the Marta River. Fertilizers are a second source of contamination. The chemical content of the lake is monitored at several stations around it.