Ruthless River by Holly FitzGerald
In 1973 "Holly and her husband, Fitz--married less than two years--set out on a yearlong honeymoon adventure of a lifetime, backpacking around the world. Five months into the trip their plane crash lands in Peru at a penal colony walled in by jungle, and their blissfully romantic journey turns into a terrifying nonstop labyrinth of escape and survival.
"On a small, soon-ravaged raft that quickly becomes their entire universe through dangerous waters alive with deadly animals and fish, their only choice: to continue on, despite the rush of insects swarming them by day, the sounds of encroaching predators at night. Without food or means of communication, with no one to hear their cries for help or on a search-and-rescue expedition to find them, the author and her husband make their way, fighting to conquer starvation and navigate the brute force of the river; their only hope for survival, in spite of hunger and weakening resolve, to somehow, miraculously hang on and find their way east to a large riverside town, before it is too late..." --from the publisher
This is a great story that is told pretty well. It's a quick read with all the necessary elements of adventure of a survival story. Neither of them had survival training nor much survival instinct, and their rescue is nothing short of a miracle.