Otter Lake is a 765 acres reservoir in Macoupin County, Illinois. It is located 6 miles west of Girard. The reservoir is named after Otter Creek, a tributary of Macoupin Creek and the Illinois River. Otter Creek was dammed to provide flood control, water-based recreation, and a source of clean water for North Otter and South Otter Townships within Macou…Otter Lake is a 765 acres reservoir in Macoupin County, Illinois. It is located 6 miles west of Girard. The reservoir is named after Otter Creek, a tributary of Macoupin Creek and the Illinois River. Otter Creek was dammed to provide flood control, water-based recreation, and a source of clean water for North Otter and South Otter Townships within Macoupin County. Recreation centers on fishing opportunities, with the lake managed for striped bass, crappie, and muskie.