|Trophy: Swimming Hole|
|Complete 'Reach Metal Head area via sewer'.|
One inside the Sewers, take a right and cross the pipes that release toxic gas now and then. Through the door, you will encounter roboguards, all easy prey to the Beam Reflexor though the Arc Wielder with robot shock upgrade is a good choice as well. Continue on until you reach a moving platform, where some hover guards attack you; their behavior is similar to wasps and the two weapons mentioned before should be used here.
Up ahead through the deactivated electric fence is another room where several more hover guards attack. You're trapped in this room (the fence deactivates when all the enemies are killed) with little space to move. The next trap consists out of a rather slow ambush with numerous spydroids climbing up from below. The Wave Concussor works well against these. As you go onwards and step on the moving platform, you are going to be shot at by a turret up ahead halfway through. Jump to dodge the bullet as the turret moves sideways.
The room on the left has a body of water filled with saw fish; don't enter while they are still around. Instead, wait around until all of them have climbed on top of the platform and died trying to attack you (use the Scatter Gun for low effort requirement). After that, jump into the water and swim underneath the metal barrier. On the other side, press a button to fight off more saw fish.
The following room is a square, within a square, within a square, with the outer two squares being patrolled by one blade beater. Jump into the water to avoid them with ease. The next and last room has a couple more hover guards in store. When you go up the elevator, you'll automatically begin the next mission: "Destroy dark eco tanks".