1. To indirectly cause the destruction of an aquatic community by allowing substantial amounts of fertilising compounds to enter a clean body of water such as a pond or river.
2. To drop a deuce into a pond or river. Implies that the resulting noxious log will kill all the fauna.
Man: Fucking hell son, what did I tell you about shitting in the sea? Do you want to eutrophicate it and see all the fishes die?