How about something where a voodoo priest/priestess remarks at the beginning of the ride that, since the river is sacred, we are violating their holy rites and grounds. Then I have one word for you...
Nothing gets them like flesh-eating zombies! Have rise out of the water and rock the boat! You have have the skipper shoot a few in the head with a delicious ker-plunk!
Yes, not for the kiddies, but hey...figured it'd be in the 'spirit' of things. And how 'unPC' can you get with voodoo?