According to the Manual (found here: support.garmin.com/support/manuals/searchManuals.faces ) the watch is waterproof to 50 meters. This considerably more waterproof than the Foretrex 201 we used in the past which had very poor water resistance. Most of these died very quickly if they were not protected with a waterproof bag.
Base on that I might be temped to try it.
Remember is is not approved for posting on GPS windsurfing websites, even if you could get the data out of it. But for purely monitoring distance it might work OK.