This is the discussion for A Nancy Drew and Hardy Boys SuperMystery'88 book "High Survival" from August 1991.
From what I recall of this offhand, it took place largely in the outdoors and Frank, Joe and Nancy go whitewater rafting at one point, I believe it is. The setting alone gets me interested- the outdoor in the woods-type stories are pretty fun. :)
I'm reading it right now and it takes place in the Wyoming mountains with Nancy and George going on a hiking trip with a bunch of kids from all over the US, and the several mishaps happening and Nancy calls the boys for backup.
I do recall now that you mention it that Nancy calls in Frank and Joe to help her. That's cool- that probably makes this book one of the few times where Nancy calls Frank and Joe to come help her on a case. (And of course, Frank and Joe have sometimes called Nancy to come help them on a case in some books in this series too.)
Thank you for starting the topic for me, I had several projects to work on, altough I had chosen High Stakes, not High Survival.
Guess I got the two similar titles mixed up