Above, Illinois Natural History Survey laboratory and instrument pier on Ridge Lake, Fox Ridge 
State Park, near Charleston, Ill. This new 18-acre artificial lake is an experimental area for 
limnology and fish management studies. The laboratory is equipped for many phases of lake 
work and also furnishes living quarters for Survey technicians. The instrument pier, in lake at 
left, houses recording instruments for air and water temperatures, a rain gage, a water level 
recorder, and wind direction and velocity indicators. Ridge Lake, which was stocked in the 
spring of 1941 with largemouth bass only, was opened to aaa fishing in 1942. 
Below, the dam aug outlet tower at Ridge Lake, April, 1941, when the lake was beginning to 
fill. The tower s designed to take care of small rises of water. The water enters the tower 
at its base, and, eA the lake level reaches a point about 3 feet from the top of the tower, the 
water spills over a partition in the tower and flows through a concrete tunnel to the other side of 
the dam. A surface spillway (not shown in illustration) carries off flood waters. A valve at 
the base of the tower allows the lake to be completely drained. The face of the earth dam is 
shown being rip-rapped with concrete blocks to prevent washing. 
