I'd suggest, Danny, to always consult with a lawyer for stuff like that and how the law applies to your particular site and specific situation.

But on the whole would offer up California and New York as being the only states here in the US in which someone would want to host the stuff.

US laws concerning what is wrongly obscene and what can be allowed depends on the definition of obscenity within ones own particular community. So obviously a place like San Francisco would have a different take on watersports than a place like Bumbleweed, Alabama. Know what I mean?

And that's really what it comes down to... community standards. Explicitly, California and New York have no prohibition of watersports and companies like Penthouse (operatng out of NY) and Flynt Publications (operating out of CA) consistently and regularly produce and distribute watersports content.

So again, US laws on obscenity are just vague at best. So the factors you'd have to consider would be community standards and the TOS of hosting companies, billing companies, etc.

What's kinda used as the default list of no-go US states when it comes to stuff like this is:
ALABAMA
FLORIDA
KENTUCKY
MINNESOTA
MONTANA
NEBRASKA
NEW YORK
NORTH CAROLINA
OHIO
OKLAHOMA
TENNESSEE
UTAH
VIRGINIA

because legal precedent in those states has made it unwise to release that kinda stuff there.

Again, though, it'd really be best to check things out with a lawyer because every individual site and company's situation is different and unique.