It's quite dynamic stage, where you won't have time for thinking about tactical solutions, therefore I recommend to read the whole level's description and getting know of the map, before you'll start playing.
At very beginning, when you'll swim from behind the bend on the left side (moving back to the trend of flow - walk like this all time), the rapid will show up and attack you. If you don't stop it earlier, he'll eat you so throw bone at him (a few seconds for preparing one). Then fire a few shots, when he'll be chasing you in the river.
Swim under the stone construction to block the reptile. He'll move on the ground again and walk round the obstacle. The flying monster will scare away from the mentioned construction and attack, so eliminate him before the second assault of the gigantic reptile.
As you've probably noticed already (or know it, if you're reading the text before playing), the second rapid will show up, walking on the other - right - side. Concentrate your attention on him now.
Swim under next stone construction and you'll fall down from small waterfall. You'll have two task to fulfil now. First, fight off the next flying creatures (about five of them)...
...after that, light grass up on the right side, in order to block the rapid's way. Try to do it quickly (there're two separate acres of grass).
When grass will be set on fire, the 'right' opponent will attack farther, near water, taking the 'grey' passage between rocks. Fire a few shoots at him.
Now, quickly look at the other rapid. He'll walk down from small raising and get near your grass. If you don't stop him, you'll be immediately eaten.
After fighting off the attack, swim into the cave, where you'll be safe.
Someone will notice, that there's an enemy already waiting for you at the exit (turn in flow's direction now). You'll be lucky, because Kong will join he action (Ann in his hands) and probably save your skin this time.