A thick, floating mat of green or reddish plants slowly covers the surface of your dam or lake. You might have seen it before. At first, it might seem harmless, or even attractive on top of the water. But if that plant is Azolla, you’ll want to act fast.
Though Azolla has some environmental benefits, it can quickly take over a waterbody if left unmanaged.
It blocks sunlight and limits oxygen, which suffocates the aquatic life below. The result? A choked dam, unhappy livestock, and costly clean-ups down the line.
In this blog, we’ll explain exactly what Azolla is, why it spreads so quickly, and the most effective (and sustainable) ways to control it.
What Is Azolla?
Azolla is a small floating fern that naturally grows in Australia’s waterways. It’s usually found in calm or slow-moving water like farm dams or ponds, and in wetlands or billabongs. Azolla grows well in warm, nutrient-rich water, especially in places with a build-up of waste or fertiliser runoff.
The two main species found in Australian dams are:
- Azolla filiculoides: People also call it red Azolla because it often turns purplish-red in direct sunlight or cooler weather.
- Azolla pinnata: It has a feather-like look and is a bit more lobed.
They float freely on the surface with their roots hanging down into the water, forming thick, interlocking mats.
What Does Azolla Look Like?
Azolla is tiny, but it grows rapidly and in dense clusters. You’ll notice:
- Small fern-like leaves covering the water like a blanket
- Colours ranging from deep green to reddish-brown
- Water underneath becoming shaded, often with dying vegetation below
When it spreads, it blocks sunlight and lowers oxygen levels, leading to an unhealthy and unbalanced waterbody.
Is Azolla Always Bad?
Not necessarily. When kept in check, Azolla can:
- Provide habitat and shelter for aquatic life
- Help absorb nutrients and filter water naturally
- Offer food for fish, insects, and water birds
- Be harvested for use as a nitrogen-rich fertiliser
But the key here is balance. Once Azolla takes over, these benefits quickly turn into major risks. Without light and oxygen, fish and underwater plants start to die, water quality gets worse, and your dam can turn into a thick, nutrient-filled mess.
How to Remove Azolla From Your Dam or Lake
Controlling Azolla effectively requires a multi-step approach. With mechanical removal, nutrient control, aeration, and probiotic treatments, you can get it under control — and keep it that way.
Here’s what we recommend:
Step 1: Mechanical Removal (The Right First Move)
If your dam or lake is blanketed in Azolla, your best option is to start with physical removal. This clears the thick surface mats, reduces biomass, and makes follow-up treatments much more effective.
Why this step matters:
Spraying herbicide on large areas of Azolla may seem like a quick fix, but it often does more harm than good. When the plants die, they sink and rot at the bottom, releasing nutrients that feed new growth. Removing Azolla by hand or machine stops this from happening.
How to do it:
- Manual Skimming: For smaller infestations, use pond nets or surface skimmers to remove floating mats by hand.
- The DeSkuzzer 2.0: This lightweight skimming tool is ideal for dragging large patches of floating weeds to shore without heavy machinery.
- Weed Booms: These floating barriers help trap Azolla in specific areas, making it easier to isolate and collect.
- Mechanical Harvesters: For large-scale outbreaks, professional removal is the most efficient option. We often help coordinate mechanical removal for clients before any chemical or biological treatments.
Step 2: Probiotic Treatment with Biostim
Once the majority of the Azolla has been cleared, the next step is to treat the water itself, otherwise, it will likely return.
This is where Biostim comes in. It’s a natural probiotic blend that boosts beneficial bacteria in your dam. By consuming the nutrients Azolla needs to grow, mainly nitrogen and phosphorus, these microbes help restore balance to the ecosystem.
Why Biostim works:
- Limits Azolla regrowth by reducing nutrient levels
- Improves water quality by supporting “good” aerobic bacteria
- Safe for fish, livestock, pets, and wildlife
- Completely natural with no chemicals
We recommend applying Biostim monthly, especially during warmer months when growth is most aggressive.
Step 3: Aeration to Support Good Bacteria
Biostim works best in oxygen-rich water. That’s why aeration is another critical tool in your Azolla control plan.
Benefits of aeration:
- Raises dissolved oxygen to help beneficial bacteria
- Speeds up breaking down organic waste
- Disturbs still surface water, slowing Azolla spread
- Enhances overall water clarity and quality
- Surface aerators: Ideal for deep dams, sub-surface systems pump air from the bottom
- Sub-surface systems: Perfect for remote or off-grid locations, solar or wind-powered models are available.
- Solar or wind-powered models: Mix the top layers of water.
Step 4: Spot-Treat With Herbicide (If Needed)
If a little Azolla grows back after you’ve removed it, you might need to use herbicide. Just make sure to follow the local Australian rules and use it safely. For this, you can use aquatic weed killer by WaterTreats or other herbicides, like the Knockout Aquatic Herbicide for the same effect.
When we handle projects, we only use herbicide at the end, after most of the Azolla is gone. This way, we cut down on chemicals and stop new blooms from growing on the dead plants.
Pro Tip: Use Biostim Accelerator with herbicides to make them work better. It breaks down the slime on plants, attacks spores and seeds, and helps you use less chemicals overall.
Long-Term Prevention Tips
Azolla thrives on excess nutrients, so keeping your waterbody healthy is the key to prevention.
Here’s how to stop it coming back:
- Apply Biostim monthly to keep nutrient levels in check
- Use weed booms to contain and control new growth
- Install an aerator to help maintain a healthy ecosystem
- Plant vegetation buffers around the dam to filter runoff
- Remove dead leaves, manure, and plant matter from the water regularly
- Avoid over-fertilising nearby land
- Provide off-dam watering for livestock to reduce contamination
Final Thoughts
Managing Azolla doesn’t have to be a constant struggle. You can restore your dam or lake to a clean, balanced, and thriving waterbody that supports livestock, wildlife, and healthy ecosystems with the right approach.
Need help restoring your dam or lake? Get in touch with us today for free expert advice and start working toward a smarter, sustainable solution.