How to Get Rid of Pond Weeds

To get rid of pond weeds for good, you have to do two things: remove the plants you can see and cut off the nutrients and sunlight that let them grow back. For small garden ponds, physical removal with a skimmer net or rake, followed by aeration, a bit of shade and less fish food, solves most problems. For larger farm or backyard ponds, combine raking with biological controls such as pond dye, beneficial bacteria and, where legal, sterile grass carp. Aquatic herbicides work fast on duckweed, watermeal and dense submerged weeds, but they must be labeled for aquatic use, applied to part of the pond at a time to avoid oxygen crashes, and are regulated in some states. Identify the weed first, because the right fix for duckweed is very different from the fix for coontail or hydrilla.

Part of our Ponds & Water Gardens guide →

In this guide

1. Identify Your Pond Weed
2. Why Pond Weeds Take Over
3. Method 1: Physical Removal
4. Method 2: Reduce Nutrients and Light
5. Method 3: Biological Control
6. Method 4: Aquatic Herbicides
7. A Season Plan for a Weed-Choked Pond
8. Special Notes for Garden and Koi Ponds
9. Preventing Pond Weeds From Coming Back
10. Frequently Asked Questions

Identify Your Pond Weed

Weed	What it looks like	Type	Best control approach
Duckweed	Tiny round green leaves, 1/8 inch, with a single dangling root; covers surface like a carpet	Floating	Skimming, nutrient reduction, aeration, herbicide for large ponds
Watermeal	Even smaller, grainy green specks like cornmeal, no roots; feels gritty	Floating	Same as duckweed; harder to remove, often needs repeat treatment
Coontail	Bushy, dark green whorls of stiff forked leaves on long stems	Submerged, free-floating	Raking, dye, grass carp, herbicide
Pondweeds (Potamogeton)	Long stems with narrow or oval leaves, some floating on surface	Submerged, rooted	Raking, dye, grass carp
Elodea and hydrilla	Small leaves in whorls around a stem; hydrilla has serrated leaves and is invasive	Submerged, rooted	Professional management; hydrilla is regulated
Cattails and reeds	Tall emergent plants at the edge	Emergent	Cutting below waterline, digging, herbicide on foliage
String or filamentous algae	Hair-like green mats, slimy	Algae, not a plant	Raking, barley straw, beneficial bacteria, algaecide

Algae is a separate problem from true weeds and responds to different treatments. If your issue is green water or slimy mats, see our guides on controlling pond algae and string algae.

Why Pond Weeds Take Over

• Excess nutrients from lawn fertilizer runoff, decaying leaves, fish waste and uneaten food.
• Shallow water, where sunlight reaches the bottom and lets rooted weeds grow; most submerged weeds struggle below about 6 to 8 feet unless water is very clear.
• Still water with low oxygen, which favors floating weeds and muck buildup.
• Introductions on boots, nets, new plants, waterfowl and boats.

Method 1: Physical Removal

Floating weeds (duckweed and watermeal)

• Use a fine-mesh skimmer net for small ponds; watermeal slips through coarse nets.
• Skim daily during the growing season, starting from the downwind edge, where wind piles the plants up.
• On larger ponds, float a boom or a length of pool noodle or rope to corral the weeds into one corner for easier removal.
• Run a skimmer pump in garden ponds; it continually pulls floating weeds into a basket.
• Compost the removed plants away from the pond, since they are rich in nutrients.

Removal alone rarely eliminates duckweed, because a few leftover plants double quickly in warm weather. It keeps populations manageable while you fix the nutrient source.

Submerged weeds

• Use a pond rake or weed cutter with a long rope. Throw it out, let it sink and drag it back to shore.
• Work in sections, removing as much plant material as possible, including roots where you can.
• Pile weeds on the bank to drain, then remove them so nutrients do not wash back in.
• Repeat every few weeks during peak growth. Fragments of some weeds, such as hydrilla and Eurasian watermilfoil, can root and spread, so collect everything.

Emergent weeds

Cut cattails and reeds below the waterline in late summer; regrowth that is cut and drowned repeatedly weakens over time. Small stands can be dug out, rhizomes and all. Leave some edge vegetation if possible, since it filters runoff and shelters wildlife.

Method 2: Reduce Nutrients and Light

• Feed fish only what they eat in a few minutes, and less in cool weather.
• Keep a no-fertilizer buffer strip at least 10 to 25 feet wide around larger ponds, planted with native grasses.
• Remove fallen leaves before they sink; net small ponds in autumn.
• Add aeration. Diffused bottom aeration circulates water, raises oxygen and helps bacteria break down organic muck that feeds weeds. See our roundup of pond aerators.
• Add beneficial bacteria and enzyme products, which can reduce sludge and nutrient levels over time.
• Shade the water. In garden ponds, water lilies covering about half the surface shade out duckweed and algae; see how to shade a pond.
• Use pond dye in larger ponds without fish-viewing needs. Blue or black dye limits sunlight reaching submerged weeds. Dye works best applied in early spring before weeds grow, and it does little against floating weeds.

Method 3: Biological Control

• Koi and goldfish: in garden ponds, koi readily eat duckweed and can keep light infestations in check. They also eat desirable plants.
• Triploid (sterile) grass carp: in larger ponds, grass carp eat many submerged weeds, especially soft species like pondweed and hydrilla. Many states require a permit and allow only certified triploid fish; some states prohibit them. Contact your state fish and wildlife agency first. Grass carp are less effective on duckweed, watermeal, coontail and algae.
• Ducks and geese: they eat duckweed but also add nutrients through droppings, and they can carry weeds between ponds.
• Barley straw: decomposing barley straw is widely used to suppress algae in small ponds, but it does not control higher plants like duckweed. See barley straw for ponds.

Method 4: Aquatic Herbicides

When a pond is choked and physical methods cannot keep up, an herbicide labeled for aquatic use is the fastest fix. Only use products registered for use in water, follow the label exactly, and check whether your state requires a permit for treating ponds, particularly ones connected to streams or used for irrigation, drinking water or swimming.

Active ingredient	Commonly used for	Notes
Fluridone	Duckweed, watermeal, many submerged weeds	Slow-acting systemic, works over weeks; needs low water flow; treats whole pond
Diquat	Duckweed, many submerged weeds	Fast contact action; less effective in muddy water; water-use restrictions apply
Flumioxazin	Watermeal, duckweed, some submerged weeds	Fast; works best in water with pH below about 8.5
Glyphosate (aquatic formulations)	Cattails, emergent weeds, water lilies	Applied to foliage above water; does not work on submerged weeds
Copper-based products	Algae; some formulations for certain weeds	Toxic to koi, snails and some fish at higher doses; avoid in soft water with sensitive fish

Herbicide safety rules

• Treat in spring or early summer when weeds are actively growing and before they become a dense mat.
• Treat a third to a half of a heavily weeded pond at a time, waiting about two weeks between sections. Decaying plants consume oxygen, and a large die-off can kill fish, especially in hot weather.
• Run aeration during and after treatment.
• Observe water-use restrictions on the label for irrigation, livestock, swimming and fish consumption.
• Never use land herbicides in water.

A Season Plan for a Weed-Choked Pond

1. Late winter: measure the pond’s surface area and average depth so you can calculate volume for any treatment. Install or service aeration. Add pond dye if submerged weeds were the problem last year.
2. Early spring: rake out last year’s dead growth and muck from the shallows. Start beneficial bacteria once water warms past about 50 degrees F. Establish a no-mow, no-fertilizer buffer around the edge.
3. Late spring: as weeds start growing, identify them and decide on control. This is the best time for herbicide treatment if needed, in sections, while water is cool and holds more oxygen.
4. Summer: skim floating weeds weekly or daily, and rake submerged weeds every few weeks. Watch fish closely during hot spells, especially after any treatment.
5. Fall: remove leaves before they sink, cut emergent weeds below the waterline, and note which areas had the worst growth so you can target them earlier next year.

Special Notes for Garden and Koi Ponds

Small lined ponds with fish rarely need herbicides. Daily skimming, a skimmer box, good filtration, UV clarification for algae, water lilies for shade and careful feeding usually keep duckweed and string algae under control. If you must treat, choose products labeled safe for ornamental fish ponds, dose by exact pond volume, and remove dead plant material promptly. Avoid copper products if you keep koi or snails unless the label clearly allows it. Remember that new plants from nurseries and friends are a common way duckweed arrives, so rinse and quarantine new aquatic plants before adding them.

Preventing Pond Weeds From Coming Back

• Maintain aeration year-round in larger ponds.
• Keep a vegetated buffer and no-fertilizer zone around the edge.
• Remove leaves and debris each fall.
• Dredge or vacuum muck when it builds up more than a few inches.
• Inspect and rinse new plants, nets and equipment.
• Keep fish stocking and feeding in balance with filtration.

For filtration, seasonal care and building a healthier pond overall, see our ponds and water gardens guide.