Mirror lake...makes Buckeye Lake look clean
Lake? If you count "reservoirs" the closest is Griggs. Take Lane until it dead ends into 33, make a right, about a mile down on your left.
As for true lakes (Griggs is a dammed stretch of the Scioto River), prolly Hoover or Alum would be the next closest. Griggs is within a few miles of campus...as close as you'll get.