Pray for Darkness by James Michael Rice
A fiction book published this decade so not long since it's under a decade old.
The plot is straight forward Ben Sawyer and his friends are on a adventure tour in the remote section of the Amazon Jungle except the worst thing does happen because their riverboat captain so now they are stranded in the Amazon Jungle with rlthis vacation becoming a nightmare because of a battle for survival because something wicked is stalking them using the darkness as a cloak, watching them, and won't allow them to leave the Jungle alive.
So a combination of Brokedown Palace, Predator and Anaconda.
A possible animal of the Amazon Jungle is the 1 that murdered the boat captain and will kill other humans.
It's not a dull book because of the mystery add in the Amazom Jungle the Green Hell it's unlikely Ben and his friends will be able to avoid all dangerous animals.
My guess is a Jaguar murdered the boat captain, and is what doesn't want them to leave the Jungle alive add in watching and stalking them.
Jaguars live in the Amazon Jungle, they are a formidable animal because their bite is incredible since a jaguar's bite can pierce a skull.
Also they can run, and could without sweating kill unharmed humans.
I don't recall a creature feature or animal intentionally killing humans fiction story with a Jaguar so that's why it being something new and original, along with the above reasons of why Jaguar is a Formidable animal is why I'm guessing it to be a jaguar.
So far it's been entertaining and a page turner.