You might have noticed duckweed floating on the surface of your water and thought nothing of it. But do you know the harm it can cause to water? If this kind of weed is left unchecked, it can blanket the surface very quickly, resulting in the blockage of sunlight and a fast reduction of oxygen. As a result, the dam or lake’s ecosystem can collapse and a once healthy body of water can enter a state where it becomes increasingly difficult to reverse.
The good news is that you can prevent the duckweed from having this effect; you just need to know the right solutions. Targeted treatments and solid strategies will help you get rid of duckweed from a dam or lake.
Duckweed: What Is It?
Duckweed is the name for a few types of tiny, floating plants from the Lemna, Spirodela, and Wolffia groups. Even though they’re tiny, these plants grow really fast and can quickly affect waterbodies a lot.
What Does Duckweed Look Like?
Duckweed comes in the form of clusters of small, oval or round “leaf-like” structures. These are called “fronds”. About the size of a fingernail, each one is roughly 1-5mm wide. Because they look similar, people sometimes confuse them with algae.
Underneath a duckweed, there is normally a single fine root that dangles and in terms of colour, it can really vary. In some conditions it can be bright lime green or deep olive. In cooler weather or strong sunlight, they may develop red or purplish tones as a stress response.
Where Does Duckweed Thrive in Australia?
Duckweed is very common and widespread across Australia. It’s particularly found in:
- Farm dams and livestock watering holes
- Stormwater retention basins
- Irrigation channels and drainage ditches
- Wetlands and billabongs
- Slow-moving creeks, especially in agricultural areas
Places with lots of nutrients and warm temperatures are what duckweed looks for. These are often found in livestock manure or areas with decaying vegetation, so it’s good to be aware of.
People might call duckweed water lens, water lentils, or floating weed, depending on where they live. The most common types are Lemna minor (common duckweed), Spirodela polyrhiza (giant duckweed), and Wolffia (watermeal).
How to Get Rid of Duckweed From a Dam or Lake
The most reliable approach to removing duckweed for good is a combination of manual removal, nutrient control, aeration, and in severe cases, targeted herbicide treatment.
How to tackle duckweed, a step-by-step guide:
Manual Removal
One of the best things to do first is to try and manually remove as much of the duckweed you can yourself. This works well as you’re helping to clear the way for any future treatments to get to work, as well as stop decaying plant matter from sinking to the bottom and creating an even bigger problem. As decaying plant matter eventually becomes food for duckweed and other pests, which only increases the problem.
For the best results, wait until the day after windy weather. This will gather the weeds and do a lot of the hard work for you.
How to do it:
- Use a Pond Net: For small patches, gently scoop the surface using a regular pool or pond net.
- Try the DeSkuzzer 2.0: If you want to avoid getting wet or if the area is larger, the DeSkuzzer 2.0 makes collecting duckweed easier. It drags floating plants to the shore without heavy effort.
- Deploy Weed Booms: To keep duckweed contained and stop it from spreading, place floating weed booms. These act as barriers, isolating sections of weed so you can remove or treat them efficiently.
Nutrient Control: A Great Long-Term Solution
If your water is full of nitrogen and phosphorus, unfortunately, duckweed will thrive. Things like fertilisers, livestock runoff, septic leaks, or decaying organic matter can increase the amount of this nutrient. Therefore, if you can control the amounts of these nutrients in the water, you can keep on top of the issue altogether.
Introducing Biostim: A Natural Probiotic Solution
Biostim is one of the best tools for managing these nutrients. It’s a 100% natural probiotic that boosts good, oxygen-loving bacteria in your dam or lake. Good bacteria consume nitrogen and phosphorus, which reduces these nutrients in the water making it harder for duckweed to grow.
Why Biostim Works:
- Stimulates natural bacterial activity without chemicals
- Reduces nutrient levels to limit duckweed food supply
- Restores ecological balance in your waterbody
- Completely safe for fish, livestock, and wildlife
Pro Tip: Biostim works best when paired with aeration because oxygen is essential for these aerobic bacteria to thrive.
More Ways to Reduce Nutrient Runoff
Along with using probiotics, try these simple actions around your dam:
- Plant grass or other plants around the edges to catch runoff
- Use weed booms to trap debris before it enters the water
- Stop erosion on dam banks and nearby land
- Don’t use too much fertiliser near your dam
- Fix any leaking septic systems
- Take out dead leaves and plants from the water often
Mechanical Aeration: Boost Oxygen, Starve Duckweed
Installing an aerator or aerating fountain in your dam or lake is a great strategy for reducing duckweed. These devices will help to circulate water and introduce more oxygen into the water. This stimulates “good” bacteria which compete with pests like duckweed.
How Aeration Helps:
Adding oxygen to the water helps grow “good” bacteria that break down waste and use up extra nutrients like nitrogen and phosphorus. Since duckweed needs those nutrients to grow, more oxygen means less food for duckweed and it’ll slowly die off.
Benefits of Mechanical Aeration:
- Raises oxygen levels to support beneficial microbes
- Speeds up decomposition of sludge and organic debris
- Reduces nutrient availability for duckweed
- Prevents stagnant water where duckweed thrives
For best results, combine aeration with probiotic treatments like Biostim. Together, they create a healthy, balanced aquatic environment less hospitable to duckweed.
Choosing the Right Aeration System
- Surface aerators mix and add oxygen to the top layer of water.
- Sub-surface aerators push air through the bottom of the dam, which works well for deeper water.
- Solar or wind-powered aerators are eco-friendly and great for remote or off-grid areas.
Chemical Treatment: Use with Caution
For serious duckweed problems, herbicides can quickly help in large dams or lakes. But, you need to use them with caution. Australia has strict rules about which ones you can use and who’s allowed to use them, so always check the local laws first.
If you need to use herbicides, try products like WaterTreats Aquatic Weed Killer or Knockout Aquatic Herbicide. They meet safety rules and work well on duckweed and you can easily get them from LoveMyDam.
Make Herbicides Work Better with Biostim Accelerator
Using herbicides? Pair them with Biostim Accelerator to get better results with less chemicals.
Here’s how it helps:
- Breaks down dead plants faster: boosts microbes that clean up dead duckweed quickly, so fewer nutrients return to the water.
- Stops regrowth early: It targets seeds and spores to help stop weeds before they come back.
- Removes slimy coatings: Some plants have a slime layer that blocks herbicides. Biostim breaks this down so chemicals can work better.
- Uses fewer chemicals: Since it helps herbicides work faster and deeper, you often need less, which is better for the environment.
- Supports water health: Faster cleanup means better oxygen levels, which helps fish and other aquatic life.
Important Warning
We generally don’t recommend herbicides as a first choice because they kill both “good” and “bad” organisms indiscriminately. But in extreme cases, they may be your only option.
If you want to stop weeds from coming back, you need to use herbicides with aeration and probiotics like Biostim. Otherwise you’re only tackling the symptom, not the problem. Which means you’ll be dealing with the same issue again soon.
Why? Because if you don’t boost the “good” bacteria with oxygen and Biostim, the extra nutrients stay in the water. That’s food for the next round of weeds or algae, which will just grow back.
This creates a chemical cycle, you keep killing weeds, but new ones keep coming. Over time, this can have a detrimental effect on your dam’s health.
Preventing Duckweed From Coming Back
Keeping your water healthy is the best way to stop duckweed from coming back once you’ve removed it. Here’s what you should do:
- Keep aeration and water circulation consistent
- Regularly dose with Biostim to support beneficial bacteria
- Inspect water surfaces often and remove or treat any new duckweed early
- Avoid over-fertilising surrounding land
- Use floating barriers or weed booms to isolate and control new growth
Final Thoughts
Duckweed can be very frustrating. Especially the speed at which it can grow. But by using a mix of manual removal, managing nutrients, adding aeration, and carefully using chemicals only when needed, you can bring your dam or lake back to health. The secret is acting early and using a balanced, long-term plan.
Need help managing duckweed in your dam or lake? Get free expert advice today and find the best solution for your waterbody!