Mobii Motion is a completely waterproof GPS training computer which shows and records valuable real time information on speed, location, acceleration, heart rate and much much more.
A while back I decided that being able to record this information would will allow me to better document the rivers I get to kayak. Also, reviewing heart rate and accelerometer from rapids and waterfalls would be really interesting.
Have a look at the Mobii website by clicking on this link: www.mobii.com
Here is a short video of a low level run I did of the Dwars Waterfall with GPS data overlay