Kathie - I'm not exactly sure where Lake Thunderbird is, but if it is part of the Chain of Lakes, you need a letter of permission from the Division of Fisheries, DNR Region 2 - 1-847-608-3100. If it is a (non-public) waterway, you don't need permission. Aquatic weeds can be controlled mechanically, with a motor powered mechanical harvester, which can cut them to 5 feet below the surface, but would have to be done several times a summer as they continue to grow. That is actually not advised for water milifoil, which is spread worse by cutting! Dredging the area would remove the plants all together. There are also chemical controls, but you need to identify the exact species of plant for control. Checking with your neighbors and getting a recommendation for professional help would be my best advice!