Ask Mr. Smarty Plants

One of the best sources of information I could find about invasive aquatic plants is A Guide to Invasive Aquatic Plants of Connecticut from the Connecticut State Government.  They describe nine non-native invasive species that have the greatest potential to cause environmental and economic damage.  Najas minor (Brittleleaf naiad), one of the nine non-natives that they describe is often confused with the native, Najas flexilis (Nodding waternymph).  They also say that controlling the invasives once they are established is very difficult.  One difficulty in controlling them is that the seeds are inconspicuous and can be transferred easily by boats or boat trailers.  I don't know how large your pond is, but if it is small boats and boat trailers probably aren't a problem.  Mechanical control is one potential means of controlling invasive aquatic plants.  Hand pulling is the simplest option if the area is not too large or too deep to reach all the bases of the plants.  Other mechanical methods include hydroraking, machine harvesting and dredging.  These will cover greater areas but will probably be expensive and may require permits.  Herbicides have been used for invasives but they will also affect desired plant species; and, although they will probably reduce the density of plants they will not likely eliminate them.

Your best bet for finding the most successful methods of control in your area, however, is to contact the South Carolina Department of Natural Resources' Aquatic Nuisance Species Program.  You can find links on their webpage to excellent information, such as Aquatic Weed Control Overview from Clemson Cooperative Extension, that explains the control methods mentioned above as well as other methods.