Submerged plants in lakes help keep the water clear. Snails can eat these plants, affecting their growth. Scientists studied how different amounts of snails affected four types of plants in a clear-water system. They found that more snails led to less plant growth. Some plants were taller with fewer snails around. High snail numbers can harm plants more than help them, even in clear water with little plant debris. Adding snails to lakes could change the types of plants that grow there.