After years of teaching water aerobics and getting ideas from Turnstep I am finally making a submission.
This is a fun team challenge that gets your classes heart rate up. I call it the "Equipment Challenge" and I use the entire length of the pool for this one. I like to do this towards the end of class, but you can do it any time after a proper warm-up.
This is a team challenge and the point of the game is to collect as much equipment for your team as possible in the allotted time. I usually do 5 - 8 minutes.
Before class set out as much equipment on the side of the shallow end of the pool as you can. I use buoys, kick boards, noodles, etc. If your facility is lacking equipment you can collect water bottles from you class for a couple of weeks and use the water bottles (They are great to use as mini-buoys every now and then during class too.)
Divide your class into even teams- take fitness levels into consideration. You don't want all of the most fit people on one team. Assign each team a lane of the pool and have them line up in their lane at the deep end.
Stagger the start so that everyone isn't getting all jammed up at the shallow end. Start the first people, wait three seconds, start the second people, wait three seconds...and so on until everyone is heading down to the shallow end. Everyone then just continues to go on their own at their best pace.
They must water jog to the shallow end, collect one piece of equipment and bring it down to the deep end and set it on the side of the pool by their team's lane. They can not pass equipment or carry more than one at a time because this will require them to work harder and ensures a good cardiorespiratory challenge.
They continue to go back and forth until the allotted time is up. Be sure to let them know that any equipment in their hand at the time the challenge ends will be counted for their team, this ensures that they will work hard until the end.
At the end, count up each teams equipment pile and the team with the most equipment collected wins bragging rights.
My classes always have fun and work hard during this game. I'm sure yours will too.