In my neighborhood retention pond, we used to have cattails. At first, it was just a few clumps of them around the perimeter of the pond, and those clumps steadily grew larger. At that point, I'd manually remove a good chunk of them from each clump; they were easy to pull, and not too deep into the water.

Sometime later, a family of muskrats moved into the pond, and within a short amount of time. all the cattails were gone. Not a single cattail in the pond nowadays.

Excerpt from Robert Crais' "The Monkey's Raincoat:"
"She took another microscopic bite of her sandwich, then pushed it away. Maybe she absorbed nutrients from her surroundings."