In the early 90s a team of paddlers from Orion River Rafting http://orionexp.com traveled to Turkey to participate in Project RAFT's white water competition and river symposium. We arrived in Istanbul, convened and mingled with the organizers and the dozens of other teams from every continent, and then traveled overland to the Black Sea region.
The white water competition centered on various stretches of the Coruh River. Class II, III and IV rapids, though some of the rapids might have been viewed as Class V considering the remoteness of the river canyon. The Coruh was a pretty, large volume river with turquoise color. The surrounding countryside was stark, very mountainous and devoid of vegetation.
We rafted more than 20 miles of the Coruh over the course of the competition, passing several mountainside villages, but the river ran for hundreds of miles upstream and donwstream --- it emptied into the Black Sea.
For river trips in Turkey, contact Alternatif http://www.alternatifraft.com/
"River Rafting may not sound an immediate attraction for a holiday in Turkey"
- The Best Activities in Turkey | Just Scuba Diving (view on Google Sidewiki)