Here are some links to aquatic plant identification and methods of control (biological, chemical, and physical means). Prior to attempting any control measure, it is very important that you identify the plants in your pond that you want to treat. The Texas A&M University site at http://aquaplant.tamu.edu/ has color photographs that are a great help in identifying plants. Various means of control are discussed and there are links to chemical product labels.
Various effective chemical and biological treatment methods can also be found at the link to the Weed Control Guidelines published by the Miss. State Cooperative Extension Service at http://msucares.com/pubs/publications/p1532.pdf. See pages 172-178 for aquatic plants.
Remember that all the chemicals these sites list are safe and approved for aquatic use when applied according to the product label directions. Fish kills resulting from aquatic plant chemical control applications are due to a lack of oxygen not the chemical applied. Low oxygen levels result from the breakdown and decay once the plants are killed. To avoid low oxygen levels in ponds with excessive amounts of plants NEVER TREAT MORE THAN A 1/4 TO 1/3 OF THE PLANTS AT ONE TIME. Treat an area of plants, wait 10 - 14 days and treat the next section of plants. Remember that several treatments are usually necessary to kill the plants. The best treatment results when plants are treated EARLY IN THE GROWING SEASON when they are actively growing and before they have produced seeds.
MDWFP Fisheries Biologist