The Illinois Environmental Protection Agency initiated the Volunteer Lake Monitoring Program (VLMP) in 1981 as a result of growing public interest in lakes and the need to expand the state's data base on lake water quality. VLMP participants are trained to measure water transparency with a Secchi disc. The measurement, called the Secchi disc depth, is used to document changes in the transparency of the lake water. Typically, three sites are monitored in each lake twice per month from May through October. The volunteer also records a series of field observations such as water color, suspended sediment and algae, aquatic weeds, and weather conditions.