I and my wife Patricia Alexander were on the eighteenth floor of Harrah's in S. Tahoe enjoying the view of the lake and we saw what I thought at first might be someone parasailing (approximate size of a pea at arm's length). The object hovered then, so I figured it was a helicopter. Then, several times, it descended to lake level and disappeared, appearing as if it were briefly and repeatedly submerging. Then it would reappear, fly slowly along, hover, descend, and vanish again. Eventually we got tired of waiting for something else to happen and left. If it really was submerging, it could not have been a helicopter, but, conceivably, we were just losing sight of it. If it did not submerge I cannot rule out the possibility that it was a helicopter, but its behavior did not fit search and rescue, sightseeing, or police surveillance. As for water sampling, that is done cheaply and safely with a boat. Helicopters are expensive.