Fallen leaves need to be removed almost daily so they don't decay and pollute the water. If your water feature is located under a tree, consider stretching netting over the pond to catch the leaves. Anchor the netting on the side with bricks or stakes driven into the soil. Remove the netted leaves regularly so they don't shade the water garden. If the leaves sink to the bottom, remove them by hand or with a soft plastic rake. For larger ponds, consider investing in a pool sweep, which attaches to a garden hose and uses water pressure to remove debris and silt from the pond's bottom. A spa vacuum also works. Both are available from water garden suppliers.