I've watched people surf in the ocean, but I've heard some waves in lakes and rivers can be suitable for it!
I love surfing in the ocean.  Is there some sort of surfing competition at the Olympics?
actually, there is a U.S> open of suring held every year in Huntington Beach, CA
How does one join the U.S. open for surfing?  Can anyone join or do they have to be seasoned professionals in the event?
I don't think you have to be certified, but there is a professional certification that can be earned.
Question - are there many types of surfing, such as parasailing?
actually there are...there is parasailing, even kayaking is considered a form of surfing, or without a board like body surfing
And each type of surfing has its own U.S. open event?  Or do all the surfing types join together into one big event?