Altering the pond environment can be an effective solution to aquatic plant problems. Changing the habitat the aquatic plants grow in can de detrimental to their health and cause reduced numbers or even elimination of a certain plant species. This can be done changing the water level, flushing the water, shading, changing the water pattern, and dredging.
Water Level - Altering the water levels in a pond can have a negative affect on aquatic plant health because many species grow best in certain water level conditions. If water levels are raised, sunlight may not be able to fully penetrate the water column and submerged vegetation will die due to the lack of sunlight. Conversely, if the water levels are dropped, the sunlight and air can dry out areas along the edges that are now not covered by water. Without water contact the plants will die off and the sunlight will burn off the remaining vegetation. In my own experiences at a trout farm, ponds were periodically drained and cleaned; however, filamentous algae would still cling to rocks, aerators, and cages. A few days in the sun without water would burn the algae off and the pond would be new once filled again. Altering the water level can be a large project and some ponds that have a drain installed and constant water supply make this much easier.
Flushing - Flushing the water can have two benefits. First, flushing out the nutrient filled water with nutrient free water will lower the overall nutrient content in the water and help reduce the existing plant growth and help prevent future growth. Flushing can also be used to remove floating aquatic plants such as duckweed and watermeal. Again, in my own experiences, a small pond that was covered with duckweed was overfilled. The water level was raised a couple feet above normal level by covering the overflow. The overflow was then removed and much of the duckweed was washed into the marshy overflow area and out of the pond. This can also be a very intensive and large undertaking. A large clean water supply and overflow to the pond makes this process much easier.
Shading - Since the aquatic plants require sunlight for the photosynthesis process, limiting the amount of sunlight that reaches the water can decrease the amount of aquatic plant growth. This can be done with trees and shrubs naturally, or done through artificial shading. Another personal experience at the above mentioned trout farm had a side benefit for the aquatic plant problems. Several raceway ponds were shaded with a shade cloth to limit predation of fish by Great Blue Herons and King Fishers and also to help keep the water cool during the hot summer months, since Rainbow Trout require cold water to grow. A side benefit was the reduced aquatic and terrestrial plant growth. The water did not receive as much sunlight penetration and the aquatic weeds did not grow as fast or dense in these areas. The grasses around the pond also grew slower, which was not a problem for those unlucky enough to be selected for pond mowing.
Water Patterns - Altering the water patterns can have an effect on aquatic plant growth. Many of the undesirable aquatic plants that overtake a pond thrive in shallow, stagnant water. By changing the stagnant water into a moving, riverine environment, those same aquatic plants struggle to grow and survive. This process can be difficult and is best done with the addition of equipment. Kasco's Water Circulator was designed for this purpose. It creates directional flow and a riverine environment out of a stagnant pond. By adding a Water Circulator, you can successfully limit the amount of aquatic plants because they cannot thrive in moving water areas.
Dredging - Dredging is physically digging or removing sediment from the pond to make the pond deeper and remove organic, nutrient rich sediment from the pond, as well as the plants that are growing in that sediment. This can be a very intensive and expensive project because of the heavy equipment involved and the removal of the sediment, but is very successful. Dredging makes the pond deeper, thus increasing the water column. Deeper water has a more difficult at supporting plant life because not as much sunlight can reach the bottom. Dredging also removes much of the nutrients in the pond and the plants that are living in those sediments, thus renewing your pond or making it younger (see Backyard Ponds & Lakes). It is extremely important to remove the sediment far away from the pond so the water and nutrients to run back in or get washed in with a large rainfall.