The primary source of this beautiful 5.7 mile river (formerly known as Blue Run) is Rainbow Spring (formerly Blue Spring). As it makes it's way southward toward it's confluence with the Withlacoochee River, the river picks up additional water from a number of smaller springs - most notably Garfish Hole about a mile below the head spring. This 24 ft. deep spring has, in recent years, picked up the nickname, K.P. Hole (for the Knights of Pythias who used to have annual gatherings here). Nearby, a beautiful, dense, bottomland forest extending toward the north east follows the small trickle of a run from Indian spring.
Situated in the sandy, rolling highlands of the Brooksville Ridge, Rainbow spring run has a very different personality from it's sister spring, the swamp shrouded Silver 25 miles to the east. High, dry banks along most of the river bank, have allowed property owners to build homes close to the water. But, with it's exceptionally clear, blue waters and lots of birds and other wildlife, the Rainbow is still a beautiful paddle.
As with all springs, the flow rate of Rainbow spring varies considerably. Between 1965 and 1974, the flow rate ranged from a high of 1,230 ft³/sec. to a low of of 487 ft³/sec. The average was 763. Today, the average is somewhere around 500 ft.³/sec. These measurements are taken at the Hwy 484 bridge so as to include all of the lesser springs feeding the run. The temperature averages about 74ºF year-round.