People that refuse to believe in possibility are daft, just as people that refuse to believe in falsity are daft. Anything is possible, including the lack of something...Now in this particular case, if the sole pupose of this experiment was to show people that it could be fake, or to try and discredit evidence that hasn't been yet, it is an act in vain that was simply stupid. If these people are skeptics, they could better spend time and money creating a lake wide sonar/infrared/UV surveillance system. In the meantime, if it was for a good laugh, or a view into human nature, it is supportable.
Who are we to judge the actions of others? Only ourselves.