They came from jerks who hate swimming, obviously!

[Thanks for respecting her personal space, Larry! Not that Undyne seems to care, since she sure doesn't mind gripping his head and using it to stable herself every time she starts to lose her balance.]

What? Are you doubting me, punk?! I can definitely break this thing without raising a sweat! I won't even have to hit it! I'LL BREAK IT JUST BY LOOKING AT IT!!

[Okay, that last part might not work out so well.]