Dataset provides information about reactive silica (in mg Si L-1) in Lake Paione Inferiore (LPI) at different layer depths along the water column within the period 1984-2013. Data are at least biannual (late summer/autumn). In total 279 records of reactive silica in the Lake for the period are uploaded. The range is from 0.065 to 1.39 mg Si L-1 (±0.153). Lake Paione Inferiore is a high altitude Alpine lake, located 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. The Lake 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)