Go to local mfa & get their generic glyphosphate most sell 2.5 gallons concentrated for fraction of what roundup costs. Keep sprayi g will take several applications to kill new sprouts. I did tbis on 4.5 acre lake that was 1/3 takin over by lilly pads.2 years later only had 1 patch show up & quickly killed it off. Once you spray dont let lillys get wet for at least 1 day if posible. Can take up to wek to se results depending on weather. Will also lose any other vegetation but I found the grass recovered Along the edges....good luck
