My response was directed at domestic travel (Grand Canyon, AZ) that is non-SCUBA in nature. This is general watersports coverage 'D' and evac coverage 'C'. Obviously, if you are diving you want something that covers decompression (A) and snorkeling/diving (B).
Bear in mind that most rafting accidents happen on shore. You may want to check other travelers insurance to make sure that you do happen to trip on a rock and break a leg you're covered. Check out the GCPBA (they're on the MB Partners' directory). I've seen lots of discussions on their email list about supplemental insurance for river trips.For example, I don't plan on tripping on a rock and breaking a leg just thought it would be worth the small fee DAN costs to join their deal in case something did happen.