So do to a scheduling snafu our team is going to Nationals the third week of May instead of the fourth week. So what you say? The team event is on my anniversary. In a desperate attempt to avoid making some divorce lawyer a lot of money, I was going to spend an extra day in Reno and take my wife to lake Tahoe. 

Any folks have any experience with some of the whitewater rafting outfitters or have any other suggestions for a romantic one day itinerary?

If you have never tried it, go for the Tahoe balloon trip.

http://www.laketahoeballoons.com/

If she isn't deathly afraid of heights, she will really love it.

Why not just ask her if she is okay with celebrating it the following weekend; the week you were originally going to be in Reno.  Does it have to be celebrated on the actual anniversary date?  Just be honest with her.  Tell her it was something out of your control and you will gladly make it up to her when you guys get back.