[klvino]

For some small freshwater lakes, they participate in "weed harvesting" to keep waterways navigable and reduce "nutrient load" to the lake which can trigger algae blooms. The "weeds" are various forms of aquatic plants (e.g. Eurasian watermilfoil) which get removed and often transported to local farms for use as fertilizer. This isn't a very widespread practice, but has been included in education from state-level DNRs.