Pond Weeds: Control, Herbicides & Identification Guide

Submerged weeds are controlled mainly through physical removal and chemical control methods.

If your peaceful backyard pond has turned into a tangled mess of green growth, you’re not alone. I’ve helped hundreds of U.S. pond owners who felt frustrated watching their once-clear water get swallowed by aggressive aquatic plants. From disappearing fish to clogged pumps and unpleasant odors, pond weeds can quickly spiral into a full-blown problem.

But here’s the good news...

With the right identification and control strategy, your pond can thrive again. Whether you’re battling duckweed, hydrilla, Eurasian Watermilfoil or the ever-persistent American pond weed, this guide will walk you through what you need to know, based on what’s worked for my clients.

So, let’s dive in.

What Exactly Are Pond Weeds, and Why Should You Care?

As a pond specialist, I’ve seen how fast pond weeds can turn from harmless to harmful. These are aquatic plants that live in, on, or around your pond. Some, like native submerged weeds, support fish and water quality. Others, especially invasive pond weeds, grow uncontrollably, choke out native species, and destroy the balance of your ecosystem. In the right (or wrong) conditions, even our normally docile native species can present problems for the average pond.

Still reading? Good, because this is where things get interesting.

These plants come in three main types:

Submerged pond weeds grow completely underwater and often go unnoticed until they form thick underwater jungles. Examples of these are our most hated pests.

• Hydrilla, Eurasian Watermilfoil, Curly-leaf Pondweed, Coon tail, Sago Pondweed – and MANY others

• This is a very diverse group, controlling their growth depends on a positive ID and consistent and determined control strategies.

Floating Aquatic Plants sit on the surface and can cover entire ponds in green mats. There are many native and non-native examples of this form of aquatic macrophytes. Some good, some REALLY BAD.

• Totally free floating plants:  Duckweed, Watermeal, Hyacinth, Water Lettuce  

• Rooted floating plants: White & Yellow Pond Lily, Water Shield, Pennywort, Lotus, Yellow Floating Heart

• This is also a very diverse group and can get out of control if left to monopolize the ecosystem.

Emergent Plants (weeds) grow from the bottom and break through the water’s surface, often and can line your shoreline or provide wonderful diverse habitat for your fish, waterfowl and assorted other aquatic and semi aquatic denizens of your neighborhood. Once again - there are tons of examples here.

• Invasives: Cattails, Phragmites, Purple Loostrife, Sandbar Willow, Flowering Rush, Mint

• Natives: Blue Flag Iris, Pickerel Weed, Bur Reed, Bulrush, Soft Rush

Each growth form requires a unique approach, each species (sometimes) requires a unique approach.  All of these photosynthetic organisms will react a little differently to control methods. Be observant, get the plants ID-ed correctly - and you’ll find success in curating your private aquatic habitat. 

Identification Is Everything (Don’t Skip This Step)

Misidentifying pond weeds is the #1 mistake I see pond owners make.

Let’s say you’re looking at a patch of green. Is it the native and manageable American pond weed, or is it the invasive hydrilla? Getting it wrong can waste time and money, or worse, make the infestation worse. Even better – algae/moss isn’t a weed…. It’s completely different and needs to be controlled WAY differently than plants.  It can be tricky because there are some very plant-like algae out there (Chara, I’m looking at you!).

American pond weed has long stems with oval, floating leaves. It’s common across U.S. ponds and useful in moderation. But when it grows dense, it clogs the  water flow.

Duckweed, on the other hand, is a tiny free-floating, three leafed plant that forms dense surface mats, blocking light and reducing oxygen. It’s a red flag for high nutrient levels.

Then there’s hydrilla—one of the worst invasive pond weeds. It forms thick, underwater mats, spreads quickly, and can clog water systems and outcompete everything else. Hydrilla is a very big problem for our southern brethren.

You’re probably wondering: “How do I tell the difference?”
That’s where visual aids and consultation help. I recommend snapping clear photos and comparing them to verified images of pond weeds or using a professional ID service. You can also send those images to me, your friendly neighborhood Pond Biologist (joe@midwestponds.com). I have helped people from all over the nation (and Canada) take care of weed and nutrient issues for more than 20 years.

I would add pictures of all these plants, alas copyright laws forbid me from arbitrarily using pictures from the internet. As I do not normally go around taking pictures of noxious plants, I don’t have many in my photoroll, but please send me your pics - I can get you on the path to healthy clean water.

Now Let’s Talk Pond Weed Control

Once you’ve identified the enemy, it’s time for action. There are three main ways I help clients manage pond weeds, and the best results usually come from combining them.

First is mechanical removal. You can slice through and rake out weeds using tools like pond weed cutters, and rakes. These tools are a necessity for any pond or lakeshore owner, but they are best used for small areas, but it’s a temporary fix in most cases.

Next is chemical control. Selective pond weed herbicides like diquat (for fast results) or fluridone (for long-term control) are EPA-approved and effective—when used correctly. I can’t stress this enough: read the label, check your state regulations, and apply at the right time in the plant's growth cycle. Better yet… Give me a call to walk you through the dosage and method to put these down.  No sense using too much (or not enough) and having to spend more money on chemical that you have to.

The third method is biological control. Grass carp (where legal) can eat submerged weeds like hydrilla and coontail. But don’t just dump them in—stocking rates and permits vary by state.

This is what I tell clients: “Control is great—but prevention is better.” Keep your aging pond healthy with a good aeration system or fountain aerator. They are the biggest bang for your ecological dollar.

Stop the Problem Before It Starts

Even the best herbicide won’t help if your pond is constantly fed by fertilizer runoff or has poor circulation. That’s why I emphasize prevention as the foundation of any pond management plan.

Start by reducing nutrient runoff. Install vegetative buffers around your pond. Limit fertilizer use nearby. Grade the land around your pond so the water is deflected around it or at least slowed down enough that nutrients and sediment can be filtered out BEFORE they reach your pond.

Then add aeration. It’s one of the simplest ways to discourage algae and excessive weed growth. Aeration improves oxygen, promotes beneficial bacteria, and reduces the ideal conditions for weed outbreaks. Aeration also increases your fish carrying capacity along with a host of other benefits.

And finally, inspect regularly. Most weed problems start small. Catch them early, and you’ll avoid costly, time-consuming cleanups later.  A pond is a lot like your lawn, if you ignore it for a month in the summer…it will probably look horrible and require a great deal of work to get back in shape.

Here's What to Do Next

Still unsure which weeds you’re dealing with? Want help choosing the safest and most effective herbicide?

That’s exactly what I help pond owners with every day.

Check out our full guides on identifying pond weeds, invasive pond weeds, pond weed herbicides, pond weed cutters, and types of pond weed to get expert answers backed by real-world experience. Email me with photos of your situation and give me a call (833-779-2837) to talk about real solutions.

Don’t let weeds take over. Take control now.