You have a few choices of what you can do. In MN, the DNR has developed an Aquatic Plant Management Program. This requires you to have a permit to remove or destroy any protected plants in watershed. You can control the growth through Mechanical Control, or through the use of Herbicides. Mechanical removal involves cutting or pulling the plants by hand or with machinery.
Herbicide control involves using plant killing chemicals. This is applied to the pond either in liquid form, granular, or pellet form. Any use of this treatment requires a DNR permit. The cost of these methods depend on the size and type of the situation. These methods are only temporary, due to the roots still being alive.