That looks to be American water willow. Personally, I think it is great to have in a pond. It protects the shorelines from wave damage and provides really good habitat for fry and forage fish. The one issue with it is that it can limit bank fishing access and lures can get stuck in the stem while fishing. If it becomes an issue, it is easily removed with herbicide. If you have large expanses of shallow water (~2 feet or less)it can quickly take over.