My friend and I are arguing over this question. If you're in a boat on a pond and drop a large rock into the pond will the water level change? If so will it increase or decrease? What will happen if you catch a fish that has swallowed a lot of water? I said that the rock will increase the water level b/c it's like dropping pennies in a cup full of water, is displaces the same amout of water that's equal to the mass of the penny. In the case of the fish that water is taken out so the level decreases. The difference is very small though. My friend says that the water level will stay the same. Who's right?