As you did not give specific ...

As you did not give specific info on the lake, land use, etc., I'll give a general answer. The best approach would be to make sure that less nutrients enter the lake from the rivers flowing into it, which requires actions in the upstream areas of the lake (limiting leaching of nutrients into surface/groundwater). The second action is to structurally harvest the invasive plants and export these from the area such that the nutrients that these contain are lost to the ecosystem system. You actions should be accompanied by a water quality monitoring programme making regular measurements in the contributing rivers and in the lake to see if there is any progress and identify sources of nutrients. Depending on the status, rehabilitation may take many years as nutrients may also have been stored in the bottom sediment and be slowly released, and the aquatic ecosystem needs time to recover requiring a return to nutrient concentration levels perhaps below initial levels.