Water Hyacinths, Water Lettuce, Sensitive Ferns 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 and above. Make sure your water temperatures have warmed up before adding them to your water garden in the spring. All Water Lettuce and Sensitive Ferns will not tolerate cold water. Water Hyacinths and Frogbit will be okay at water temperatures of around 59-60, but they will not spread until the water warms up.