der Opfer also means "the sacrifice" ot "the offering". which doesnt make the sentance any less unheimlich (creepy)... that Owl has been watching true detective
I believe it is "das Opfer" and would like to add that throwing sacrifices seems like a pretty sound method to keep the lake monsters at ease, well and obviously very efficient. I mean when was the last time we saw the monster leave the lake angrily. Never! Sacrifices, that's why!
The problem is in the translation suggestion... Actually, there's no verb in German for "floating". Schwimmen stands for both, swimming and floating. In this case "the victim floats in the lake" makes more sense (creepy anyway). Another example is "Die Nudeln schwimmen in der Suppe"