The first reservoir in Eden Park was completed in 1872. The second reservoir was completed in 1878 and was called the Lower Reservoir. A carriageway named for David Baker Pass, President, Board of Public Works ran along the south wall of the reservoir. These basins were cleaned in alternate years and everything was found from wrecked cars to suicide victims. When ever this cleaning took place municipal picnics, complete with music and dancing were held inside the empty basin. Although chemical purification of city water began in 1907 at the new water plant upriver at California, the Eden Park reservoir remained in use. In the 1960s the stone retaining wall of the lower/eastern basin was largely removed and the basin was filled in for ball fields. The upper/western basin was made deeper to increase its capacity to 80,000,000 gallons. The reservoir was used until 1965 when it was covered with a shallow 3/4 acre reflecting pool, Mirror Lake.
References: http://queencitysurvey.blogspot.com/2008/01/eden-park-lower-reservoir-then-and-now.html
http://www.cincinnativiews.net/Eden%20Park%20part%203.htm