Water lilies are extremely hardy and have a tendency to grow excessively. In the image above, you can see how more than half of the pond is occupied by lilies. This reduces the space that the fish can swim around in and gives the pond a messy, unkept look. You can also see how low the water level is due to all the lilies absorbing the water. The only safe way to remove these lilies is to carefully hand-pull them from their roots.