Here is a robotic eel capable of pinpointing sources of water pollution. The Envirobot was developed by researchers from EPFL. It swims through contaminated water to find the source on its own. It can also be controlled remotely. The robot generates maps of water conductivity and temperature.
According to the researchers, the robot has chemical, physical and biological sensors to get the job done. It has a modular design, each with a motor to move smoothly through the water. More info is available here.