Quick answer: Pond management has four steps: identify what is growing, reduce the nutrients feeding it, choose a control method that fits the plant, and confirm permits before anything is applied to the water. In New York, many aquatic pesticide applications require a DEC permit.
What is growing in my pond?
Control depends on correct identification. Pond growth falls into four groups:
- Algae. Green water (planktonic algae) or floating mats and strings (filamentous algae).
- Floating plants. Duckweed and watermeal, which can cover the surface like a green carpet.
- Submerged plants. Rooted underwater growth such as Eurasian watermilfoil, fanwort and hydrilla, several of which are invasive.
- Emergent plants. Shoreline growth such as cattails and phragmites.
Some native plants are valuable habitat and help keep water clear. The goal is balance, not a sterile pond.
Why is my pond overgrown?
Nutrients, mainly phosphorus and nitrogen. They arrive in lawn fertilizer runoff, leaves and grass clippings, goose droppings, eroding banks and septic influence. Shallow, warm, sunny water makes it worse. If the nutrient supply is not reduced, growth returns after every treatment.
What are the control options?
- Nutrient reduction. Unfertilized, unmowed buffer strips along the shore, and keeping leaves and clippings out of the water.
- Physical removal. Raking, cutting or harvesting. Immediate, but labor intensive and some plants spread from fragments.
- Aeration. Improves oxygen and circulation, which can reduce algae and odors over time.
- Biological control. Triploid grass carp eat certain submerged plants. Stocking them in New York requires a DEC permit.
- Aquatic herbicides and algaecides. Effective when matched to the plant and applied by a certified applicator using products labeled for aquatic use.
Do I need a permit?
New York regulates pesticide use in surface waters, and many pond and lake treatments require an aquatic pesticide permit from the Department of Environmental Conservation. If the pond is part of or next to a regulated wetland, separate approval may be needed. A contractor should check this before quoting treatment.
Why not treat the whole pond at once?
When a large amount of plant material dies at one time, its decay uses up dissolved oxygen, which can kill fish. In warm weather, heavily infested ponds are usually treated in sections, with time between treatments.
Related: Wetland vegetation management | Surface water management | Aquatic services
This article is general information. Regulations change, so confirm current NYS DEC and local requirements. Pesticides must always be applied according to the product label.