At hydrothermal sources such as Black smokers emit hot fluids up to 400°C, which differ significantly physically and chemically from the surrounding seawater. This fluid dilutes immediately upon exit from the hydrothermal source with the seawater present in almost infinite quantities. But even the smallest changes in chemistry (e.g. pH value) or physics (e.g. temperature, cloudy, electrical potential) can be detected with modern technology. These so-called "plumes" spread over significantly longer distances than the actual field of hydrothermal activity from which they originate. Once discovered, we then try to chase after the origin of the "plum". This is done with water samples using CTD-Rosette, Tow-Yos and MAPR (Mini-Autonomous Plume Recorder) and the AUV, which is routinely equipped with special water sensors.