I dont think it's a sponsored event, it's just a bunch of people who get together and go boating.
The only limitations are ice (if present) and your willingness to deal with and ability to fight off the cold. Wear a drysuit, dress warm, and you should be good to go. After all, it is only Shoshone, not Gore.
"Don't f$&@ing eddy out, just run it! Whaddya doin??" -LMyers