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. The purpose of the VLMP is to involve volunteers with lake monitoring, thereby providing effective public education in lake ecology and management as well as a useful data base for site-specific and statewide lake quality assessment. VLMP participants are trained to measure water transparency with a Secchi disc: an eight-inch round metal plate painted black and white in alternating quadrants, attached to a calibrated rope. The disc is lowered into the water and the depth at which it disappears is recorded. 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.