Rafting/kayaking on the 'Luva & Navua Rivers nr Pacific Harbour

Is Rivers Fiji the only company that offers these tours?

No, there are a few smaller companies doing different styles of tour, some are more like village visits with a waterfall swim, others are full day paddling.

Rivers Fiji is the biggest operator I think, and its the one we personally went with. I can highly recommend their Kayaking trip, it was relatively pricey but was great fun. Take your camera, they provide dry bags so it wont get wet, and the scenery is amazing.