Water lilies are a beautiful addition to a water garden and can promote a feeling of calmness and serenity when the are healthy. Water lilies are susceptible to damage from aphids, most notably a species called rhopalosiphum nymphaeae that attacks aquatic vegetation. Aphids suck sap from the plant, which causes the greenery to wilt and curl. Several types of deterrents can be used to kill aphids that feed on water lilies.
Spray your water lilies with a garden hose; the force of the water will knock the pests off the plant. Once in the water, the aphids will most likely be eaten by fish or other creatures living nearby. Water does not hurt the plants, so this method can be used as often as needed.
Remove your aphid-infested water lilies from the water source and place them in a bucket of water.
Kill aphids with an insecticide soap. Soaps of this kind contain potassium salt of fatty acids, and are similar to dishwashing detergent. Spray the plants with a diluted, 2 or 3 percent concentration liquid. Make sure you are not using a product that contains pyrethoids if you have fish in your ornamental pond, as this chemical can also kill fish.
Hose off the treated water lilies within two hours of spraying with insecticide soap to minimize leaf damage that can sometimes occur during the treatment process. Return the plants to the water after rinsing.
Read the directions of the insecticide you have chosen to know when to apply the next treatment. Some soaps are longer lasting than others, and may need to be re-applied after a few days.