Im a huge fan of surfing, here in FL, we actually do a lot of river surfing.
Cool I've never heard of river surfing.  Does that involve a sail?
No basically the water flows over a rock in high volumes causing a wave behind it.
Interesting.  What rivers in Florida have the best river surfing conditions?
The Hillsborough River is very good for river surfing. Oddly enough, in Germany is where you can find the worlds largest urban river surfing spot.
Are there river surfing competitions?
Not at the Hillsborough River, it's amazing how old it is though, geological surveys indicate its around 27000 years old.
That's incredible.  How do they calculate the geological age?
By looking at sedimentary rocks in the riverbed, it requires hours with very powerful technology.
What type of technology is used?