h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

How about Octopush - basically v. similar to Underwater Rugby, but its underwater Hockey - played with 18" long sticks and a heavy metal puck (usually covered in plastic so as not to damage the pool bottom). Players wear Snorkels, Masks, Flippers and some type of glove - usually a gardening glove to protect their Knuckles. Idea is to score as many goals as possible. There are actually Professional Leagues for this in the States.

Also How about Canoe Polo - played in swimming pools - the goal is suspended a few feet above the pool and you have to throw the ball through it. Much fun is had by overturning competitors Canoes and watching them try and right themselves again.

I thought canoe polo was like ice hockey, less a spot more organised violence

Ive played canoe polo on a river before. We changed ends at half time so that each team got the advantage of the current. Youre right, it is very violent. Most of the people playing were not experienced Canoe/Kayakists and i personally nearly drowned myself after a small incident of having my kayak capsized and hitting my head on the bottom. We played with large nets hung over the river on ropes and the best way to score was by hitting the ball with your paddle so it went in. Unfortunatly, in the heat of a game, peoples heads and the ball often end up in roughly the same place so a good helmet is essential....

Quite!

But great fun nevertheless - slightly less so if you panic and can't remember how to roll your kayak upright again!

I almost got involved in the anual canoe polo thing the club I'm a member of has. I found it was a pleasant way of spending a sunday afternoon - watching everybody else!
The thing with polo is that remembering how to roll your kayak is fine when you still have hold of your paddles. Not always the case
Still helmets with face guards, scary stuff.

Face Guards!!! We never got face guards when I used to play - mind you seems like a good idea!