There are several chemical treatment options available for aquatic plant problems. Some treat certain aquatic plants better than other treatments, and since there are many types of aquatic plants, it is a good idea to talk with a local lake management professional to get some assistance in identifying the type of aquatic plant problem and develop a plan for the best solution to that problem. Typically, liquid treatments are more effective in shallow applications of 5 to 6' or less and granular applications are better in deep water. Granular applications can also be used in spot treatment. Some common chemical treatment methods are copper products, diquat herbicides, and fluridone herbicides.
Copper - Copper is usually the first answer most people get when they bring up the subject of algae and control. Copper is toxic to certain species of fish within the minnow family as well as salmonids depending on the dosage and water chemistry. Water with high hardness and alkalinity buffers copper from being toxic, but also limits its effectiveness. The most common form of commercially available copper is granular copper sulfate. Its effectiveness and cost as a broad spectrum controller of planktonic and filamentous algae has led to its high usage. Liquid chelated copper products are used to control a broad range of algae including planktonic, filamentous, and bottom attached types of algae. Cutrine-Plus® is an example with application rates from 0.6 to 1.2 gallons per acre-foot of water treated. Consistent usage of some copper products can lead to bioaccumulation within the sediments and this approach is on the radar of some regulatory agencies, so a varied approach is probably the most sensible path to take.
Diquat Herbicide - Diquat is a liquid, contact herbicide that is sprayed on the vegetation. This is a very powerful and fast acting form of aquatic weed and algae control. The treated vegetation will quickly die and turn brown from this treatment. A common diquat herbicide brand is Reward® and is great for floating aquatic vegetation. It is safe to use, according to the label, for algae and floating aquatic vegetation control in natural ponds, but there are restrictions concerning fish harvesting. A lake management professional will be able to assist with information and application of this product.
Fluridone Herbicide - Fluridone is a liquid, non contact herbicide that is slower process than the diquat herbicide, but does not have the same restrictions for water usage afterwards. Fluridone herbicide is sold under the product name of Sonar® and manufactured by Avast® and typically takes 30 to 90 days to effectively work. The herbicide is absorbed into the plants and symptoms develop within 1 to 2 weeks. Affected plants will lose their green pigment and turn white. This can be a more selective method of treatment depending on application levels.