I thought I had read that the dead plants started building up with sediment which over years could make the pond shallower. I love the look of a pond with cattails plus it keeps those wandering fishermen off the pond when they have no place to cast from. Me I have a boat so not a problem. I think it would probably be in my ponds best interest to remove them. I have a very sandy soil and have a feeling they are going to spread quickly. Thanks for all the information !!