You will meet Jeff Brown, who warns you against entering the jungle in the face of possibly becoming lost. But you must enter anyway so that you don't lose the enemy's tracks. When you start off, you will face a few women assassins. After you clear them away, or run past them, you will start to encounter bazooka guerrillas. Be careful when facing them, and use the same technique you did in Greece: squat low to avoid most of the blasts they shoot, and fire at them between blasts. A female assassin will appear between the first few bazooka guerrillas.
Before you reach the very end of the jungle, you will see a line of trees that extend from the background into the foreground. When you see a gap between two trees in the foreground, push to access the jungle interior. Begin walking to the left. Just when you see a mine on the floor, an enemy agent will appear and fire. Remove him, and jump over the mine. After a few more mines, another agent will appear. This will be the last enemy before an ambush. Continue to leap over the mines until you get deeper into the jungle. Eventually, a gun will appear and you will be ambushed.
This is a particularly difficult ambush, consisting of six bazooka guerrillas. They fire frequently, and the rockets they fire do a lot of damage. It's quite common to end up dying in this fight a few times before successfully making it through. You'll have to find and destroy the guerrillas as quickly as you possibly can. Shooting down the rockets isn't a bad idea either. Keep moving to the left or right until you locate and defeat all six guerrillas. When you are returned to the jungle, you will see another line of trees extending into the distance. There will be two trees way off in the background. Stand between them and press to exit the jungle.
You will arrive beside the Amazon River, and you will encounter Eve Christy. She explains how the enemy organization killed her parents, and she has been trying to get close to the leader in order to extract her revenge. She will tell you that you can reach the leader through a passage on the river, and she gives you scuba gear. You will jump in the water and swim to the right. The water here contains the usual enemy divers, but it also contains piranhas and crocodiles. Neither one are particularly dangerous, and you can swim to avoid all of them if you are careful. Along the way. you will be ambushed by seven divers.
When you reach the end of the swimming section, you will return to land and be greeted once again by the small mob boss. After an idle threat, you will begin Act 9.