A few years back, we rented a house in Florida. I really enjoyed living there, it had a natural pond in the yard and tons of wildlife, right in the middle of the city. Anyway, a few years before we rented it, there was a flood, and a neighboring pond containing duckweed overflowed into the rental house's pond. Just the tiniest bit of duckweed overtook the entire thing--it looked like a putting green. We offered to buy triploid carp from the state in an effort to clean it up, or even to install some sort of aereation/fountain, or herbicide to help.