If you notice pond weeds in an irrigation pond this time of year, leave it alone, according to Lorain County Ohio State University Extension.
However, this doesn't mean that nothing needs to be done. In fact, ponds with chronic weed problems should be inspected with a very critical eye.
Weed problems may be linked to high nutrient content or lack of pond depth. Successes and failures of pond weed control should be noted so that plans can be made, and action taken, early next year to control the problem before it gets out of control.
White Amur [weed eating fish], shading materials, dredging, and nutrient load [fall leaves, fertilizers] are just a few items in the toolkit for getting ahead of pond weeds.