Man's body found floating in the Charles

Yes.

Surrounded by water and full of young people and bars right near the water.

But how do we know this guy was young? OK, let's assume for a second that he was, in fact, young and educated (and, of course, white). Still doesn't mean there's a serial killer out there, unless you're willing to ignore all the people who drown in the river, the harbor or Fort Point Channel who don't fit the criteria - and willing to assume a level of incompetence or collusion by local law enforcement staggering to consider and going back centuries.

If you're really, truly concerned about people drowning in the waters off Boston, you'd do better to volunteer or contribute to groups trying to do something about homelessness, drug addiction or alcoholism.