Humans are not attacked by sea lampreys
They can tell the difference between warm-blooded and cold-blooded creatures and exclusively hunt the latter. In fact, in the natural, they would aggressively shun humans. As a result, they have never and will never kill a human. The sea lamprey's natural nature is to cling to things, such as the glass wall of its tank, the pebbles on the sea (or lake) floor, and so on. As a result, if one is put up to a human, it will most likely latch on like a leech. Its suction is quite forceful and can be extremely painful, putting intense pressure on the area of contact. While the bite is eventually unpleasant, no one has to be concerned unless they intentionally introduce the sea lamprey.