Cooked cabbage as snail bait in a water lily pond

The water lily pond in which I grow Victoria lilies (Victoria amazonica)was suddenly invaded by water snails two weeks ago. Although the undersides of the lily leaves are thorny, the thorns give no protection against snails. A friend who was with me recommended using boiled cabbage leaves to trap the snails. We did this, placing lightly cooked leaves on the water every evening. It works. Every morning, there are dozens of snails on each leaf, which our workers remove and destroy. I do not know if we can completely eliminate the snails by repeated trapping, but the Victoria lilies have recovered.