This level is set in a sort of sewer duct. You have to advance along the duct by defeating some simple enemies and passing between the rotating blades of some propellers, without being hit. Occasionally there are pools of water, in which you will notice at the bottom right the eel that gives its name to the level and which is actually an electric cable. Every few seconds, the eel will electrify the water in the pool, so make sure you're not in the water at that moment. To cross the longer pools there are sometimes floating platforms.
You will find two forks along the way. At the first you can take the right path first, where you will find a normal box and many Nitro boxes and then the left path to continue. At the second fork instead, it is better to go left first to find the crystal at the end of the path and then go back and go right.
In the last part of the level there is a new type of action. After entering a hole in the floor you will find the detonator to blow up all the Nitro boxes. From now on you have to hold on to the blue bars above you to proceed. Advance carefully, avoiding the little robots under the bars. You will finally have to go through one last tunnel, avoiding other small robots that cannot be destroyed by your attacks, until you reach the exit room.
The bonus area is about halfway through the course and presents no difficulty.
Getting the clear gem[edit]
Finding and breaking all the boxes in this level isn't very difficult. Just be sure to explore both paths when you come to a fork in the path. If you succeed, before the exit portal you will find the gem.
Getting the green gem[edit]
To get this gem you have to find a hidden area. If you go right at the first fork, you'll come to what looks like a dead end, with lots of Nitro boxes. The hatch at the bottom is actually fake and you can jump through it. At this point, just follow the path and at the bottom you will find the green gem. You can then go back and continue with the level normally.