Water Hyacinths, Water Lettuce and Frogbit are excellent for filtration. Floating pond plants will spread across the waters' surface providing shade and coverage for the water gardens inhabitants. Their roots absorb nutrients from the water that might otherwise cause algae and provide hiding places for baby fish. Water Hyacinth and Water lettuce grow best in water of 65 degrees. Make sure your water temperatures have warmed up before adding them to your water garden in the spring.