This will depend on the weed species on site and the aquatic fauna on site. It may be best to have a visual survey or undertake some trapping. Based on what we record, we may either recommend waiting till water levels are lowest, spray glyphosate, and then slash once leaves are dead and drown! In some cases, the use of an amphibous harvester may be recommended.  Removing plants can result in fish and frogs to be more vulnerable to predators, and therefore to mitigate the impacts it is recommended to immediately replant with local natives