The Blue River is a 57-mile-long (92 km), two-forked stream that runs through Harrison, Crawford and Washington counties in Indiana. The headwaters of the North Fork arise near Salem in Washington County and flow south, and the headwaters of the South Fork arise near New Liberty and flow southwest. The two small forks converge in Fredericksburg. From the confluence, the river flows south until it joins Ohio River in the Harrison-Crawford State Forest, just upstream from Leavenworth.

Harrison Spring is the largest spring in the U.S. state of Indiana. It is located in west-central Harrison County, near the Blue River and just north of White Cloud.