Walk the plank - a great idea for our pirate party! We had a Pirate swimming party and put the across the baby pool. The kids had to walk the plank without falling in the water. It was the best part of the party.
Recycle old water bottles and grab some cheap pool rings. You could color the water like the rings too make a more challenging match/ring toss games for the older kids. Add glow sticks for night time ring toss