Colombia has some excellent rivers for rafting, and some reliable operators to take you there. The rafting industry in Colombia is centered in and around San Gil, where local operators generally will take you to one of three nearby rivers: Fonce, Chichamocha, or Suarez.
The Fonce River has a good mix of rapids, with long sections of everything from class II to class IV rapids. Short trips can be made to the slower parts, a good option for novices or mixed groups. The Fonce can get a bit rough, too, in other sections: up to class IV, suitable for intermediate and advanced rafters.
The Chichamocha is generally a bit rougher that the Fonce, and rafting trips pass through the scenic Chicamocha canyon. The Suarez is the roughest of all. One reputable operator in the region is Colombia Rafting Expeditions (http://www.colombiarafting.com/) located in San Gil.
If you’re in Bogotá, there is some rafting to be had on the Río Negro, not far outside of town. The class III river is good for beginners.
For a slightly different rafting experience, Paisa Travel (http://www.paisatravel.com/) offers a trip on a balsa wood raft through Colombia’s coffee-growing region on the La Vieja River. The river is not particularly rough and participants are encouraged to swim off the raft as it makes its way along the river.