Lake Decatur • Built in 1920-1922 by damming Sangamon River • Primary water supply for Decatur & Mt. Zion • 3,090 Acres, contains 9.7 billion gallons of water • Two water treatment plants use 34 MGD - City of Decatur and Archer Daniels Midland • 245 days or 8 months of water supply • 926 square mile watershed • 83% of watershed used for row crops. PDF [5.19 MB]