Extreme sports such as canyoneering have expanded greatly since the turn of the century yet little scientific attention has been paid to the analyses of the dangers of those activities. The author was much involved in promoting one such sport, namely canyoneering, and presents this paper as an example of the kind of fluids engineering analyses that are needed in order to objectively quantify those dangers and properly advise the participants. In canyoneering, the primary fluid-related sources of danger are the impact of falling water on the human body and the dangers a swimmer faces in a plunge pool. This paper presents rough evaluations of both dangers.