Lake Paione Inferiore is a high altitude Alpine lake, located at 2002 m a.s.l. in the Bognanco Valley, Province of Verbania, Piedmont Region, Italy. It has a surface area of 0.86 ha and a maximum depth of 13.5 m. It is included in the monitoring sites of the UN-ECE Program ICP WATERS (International Cooperative Programme on Assessment and Monitoring of Acidification of Rivers and Lakes) funded in Italy by Ministry of the Environment and for which the CNR Water Research Institute (CNR-IRSA) is the National Focal Centre for Italy. The lake has been studied since the late 1970s in the framework of research on the effect of acid deposition on chemistry and biology of sensitive lakes. At present meteorological data are collected continuously by an automatic weather station (AWS) located on the shore of the close lake Paione Superiore. Chemical data are available since 1978 and are still collected on a regular basis (annual or biennial frequency): pH, conductivity, alkalinity, dissolved oxygen, major anions (sulphate, nitrate, chloride) and cations (calcium, magnesium, sodium, potassium), reactive and total phosphorus, reactive silica, total nitrogen, dissolved organic carbon, main trace elements (included heavy metals). Three samples are collected on the water column at the deepest point of the lake. Winter or spring samplings are performed occasionally. Available biological data include phytoplankton, zoo plankton and benthos taxonomic composition, population dynamics of the main species and, limited to 2000-2001, bacteria, epilithic diatoms, and paleolimnological data.