10 Ways to Get Rid of Algae from a Dam

So, you have an algae problem in your dam. Before going any further, it’s important to understand you’ll always have algae in your dam. Well, at least, you will if you have a healthy aquatic ecosystem. Like it or not, algae play a crucial role in maintaining a balanced ecosystem.

In fact, did you know in the US, it’s common practice to deliberately start algal blooms using fertilisers? Fisheries use these algal blooms as food for microscopic organisms, which feed macroscopic organisms, which ultimately feed fish and other large aquatic life. We say this to make it clear that reducing algae and keeping it in check is a far better goal than eliminating it entirely. 

Step 1: Understand Your Enemy

Before attacking your algae, you need to understand it. Otherwise, you’re destined to be fighting the same algae year after year. Not quite a plant or animal, algae sit on a branch of their own—the slime moulds. It’s believed the first land plants evolved from shallow freshwater algae around 500 million years ago. 

Today there are thousands of types of algae, both on land and in water. Even seaweed is a type of algae. Algae organisms range from string or filamentous algae (multicellular structures like the giant kelp) to planktonic algae (unicellular microalgae that grow in mats and often appear like pea soup).

Pictured: (Left) Multicellular “String algae”, (right) unicellular “Planktonic algae”

Step 2: Identify Your Algae

For ease, we tend to break algae down into two groups: (i) string algae, and (ii) planktonic algae. 

(i) String algae

String (or filamentous) algae looks like hair and is commonly found in relatively clear water because it needs good sunlight to grow. You can pick it up and often even take it out of the water without it falling apart. It can live on the top or bottom of your water column. It often starts growing on the dam floor—rooting in rocks, gravel, or sand—before venturing to the surface. Some types of string algae even rise and fall in your dam over the course of a day. During the day, the algae produce bubbles that allow it to rise to the surface and maximise sunlight for photosynthesis. At night, the algae release the bubbles, sinking to the floor where it can draw nutrients from the sludge.

(ii) Planktonic Algae

Otherwise known as unicellular or single-celled algae, when you get billions of these guys, it turns your entire water column green like pea soup. So, your dam is affected from floor to surface. Sometimes it can appear like a paint slick on the surface of your water. If you brush or disturb it, it might semi-stick together, but in no way will it hold together if you pull it out of the water.

Common mistaken identities 

  • Algae that look like plants: Some algae species look like plants and are commonly mistaken for weeds. Stoneworts, Chara, Nitella and String Algae are all species like this. 
  • Bacteria that look like algae: On the flip side, organisms can appear in your dam that look like algae but aren’t. Blue-green algae is an example. A deceptive name, blue-green algae isn’t actually algae, but rather a large population of cyanobacteria. These colonies of bacteria appear almost like a green paint slick on the surface of the water. This can make blue-green algae look like planktonic algae, except planktonic algae tend to occupy more of the water column, not just the surface. The good news is you can treat blue-green algae and weeds much the same way you can treat algae. So, many of the tips below still stand, especially Methods 1 and 2.

Is your algae string or planktonic?

Step 3: Find the Cause of Your Algae

Now you have an idea what type of algae you have, let’s drill down to what’s causing your algae problem. Understanding the cause of your algae is crucial to ensuring you’re not fighting the same algae year after year. If you treat the algae only (aka the symptom) and not the cause, it’s like cutting the tops off weeds without pulling out the roots. You know they’ll return, bigger and stronger.

So, what’s causing your algae problem? Answer: temperature, sunlight and nutrients. These are the 3 pillars of life for algae. When these conditions all favourably meet, we call it the Algae Growth Zone.

Without getting into specifics, the general rule of thumb is the warmer the water, the more sunlight, and the more nutrients, the greater the chances of algae. In other words, you have an algae problem because your dam’s temperature, sunlight exposure and nutrient levels are just right for the type of algae you have. The good news is this means you can eradicate your algae problem by attacking one of these three pillars.

Step 4: Plan Your Attack 

Temperature, sunlight, and nutrients are the pillars of life for algae, equivalent to air, food, and water for humans. Remove any one of these and the individual can’t survive. So, to effectively attack algae, you need to target one of these pillars. But which one?

  • Temperature is by far the most difficult variable to control in a dam; thus, we don’t recommend you try and change it. Ponds and tanks are different of course, but we’re talking exclusively about dams in this article.
  • Sunlight is a little easier to control using methods like dam dyes and lake bottom blankets, but these treatments are still quite manually intensive and difficult to apply at scale.
  • Nutrient control is by far the cheapest and easiest way to combat algae at scale and can be achieved 100% naturally; without using a single chemical. We call this “nutrient reduction”.

Nutrient reduction 101

Nutrients are being supplied to your dam all year round. These nutrients can come from runoff from roads and fertilisers, but even rainwater often has enough nitrogen in it to stimulate algal growth. Other sources of nutrients are organic materials, e.g. duck poo, plant debris, decaying animals and insects etc. This organic material enters your dam and sinks to the bottom, becoming a nutrient-rich sludge (aka fertiliser for algae). So, what’s the key to reducing nutrients? (aka what can pull nutrients directly from your water and break down organic sludge)? Answer: Aerobic bacteria.

How to reduce nutrients with aerobic bacteria

Aerobic “oxygen-loving” bacteria are the key to getting rid of your algae problem for good. These naturally occurring organisms already live in your dam, their populations are just very tiny. Encourage their populations to grow and the bacteria will consume more organic material (aka sludge) and pull more nutrients from your water. Eventually, these microbes consume so much of the nutrients, the algae starve and die.

Step 5: Attack Your Algae

Okay, theory lesson over. Let’s get practical. Below are 9 ways to attack algae. The caveat is some of the suggestions are not recommended. The simple reason is because they don’t attack one of the three pillars of life. This is why we have 3 lists below: the great, the average, and the bad. We highly recommend you choose from the ‘great list’.

Great ways to attack algae

The following algae removal methods are the only ones that ensure long-term results. They’re also all 100% natural. 

1. Aeration

Overview:

Aeration is by far the most effective way of getting rid of an algae problem for good. Remember, aerobic bacteria are “oxygen loving”, that means the more oxygen you have in your water, the larger their populations will grow. 

The most important thing about aeration is getting the right sized system to ensure you sufficiently aerate all parts of your dam, including the bottom. Otherwise, algae can still grow in deoxygenated pockets.

Application:

  • For String algae and Planktonic algae: With sufficient aeration, you’ll see results against all algae types.

2. Probiotic treatments

Overview: 

Following aeration, our number two recommendation for dealing with algae is a probiotic treatment plan. In fact, for the fastest, most reliable results we recommend pairing aeration with a probiotic treatment.

A probiotic treatment (like Biostim) involves actively feeding the “good” microbes in your dam, much the same way you might eat Greek yoghurt or drink Kombucha to feed the “good” microbes in your gut. Like aeration, this encourages populations of aerobic bacteria to grow. They eat the sludge on the floor of your dam and consume nutrients like nitrogen and phosphorus, thus outcompeting algae.

Application:


Want to chat about probiotic treatments? Scotty Tucker can provide custom recommendations based on your dam’s specs. To book a free 15-min phone chat, complete our Dam Diagnostics Survey and mention you’re interested in learning more about probiotic treatments. 

3. Floating Islands

Overview:

Floating islands are made up of buoyant mats which are planted with vegetation. The islands help with nutrient reduction much the same way as aeration and biological treatments. The key is the large, exposed root mass of the plants, which draw phosphorous directly from the water and provide habitat for bacterial populations that consume nitrogen. Less phosphorous and nitrogen in your water means less chance of algae and a healthier dam. 

When the plants have reached a decent mass, whether that’s quarterly, biannually, or annually, the plants and pots are removed and either composted or planted away from the water. This removes the uptaken phosphorus and nitrogen from your water altogether, unlike what typically happens where plants eventually die and breakdown in the water, re-releasing the nutrients back into the aquatic ecosystem. After harvest, the mats can be replanted with young, new plants using new pots and the cycle is repeated.  

There are 3 main benefits of floating plants over shore plants: 1) Floating plants pull nitrogen and phosphorus out of the water, rather than out of the soil like shore plants, (2) floating plants uptake greater amounts of nutrients than shore plants because they have more exposed root mass, 3) floating islands rise and fall with your dam’s water level so the plant roots have continuous access to nutrients in water, this is obviously not the case with shore plants.

Application:

  • For String algae and Planktonic algae: With sufficient sized floating islands (and root mass), you’ll see results against all algae types.

Average ways to attack algae

The next methods are average ways of combating algae because they focus more on the symptom than the cause. They might bring instant results, but expect your algae to reappear, unless you pair them with method 1 or 2.

4. Peroxide-based treatments

Overview:

Overseas there are peroxide-based treatments used as algaecides. In Australia, we use a similar product called AlgaeLift.  While not an algaecide, AlgaeLift helps lift algae off surfaces and makes it easier for naturally occurring bacteria to degrade it. Peroxide-based treatments are our number 4 recommendation because they can speed up the results of methods 1 or 2, while remaining environmentally friendly—because peroxide breaks down into hydrogen, oxygen and water.

Application:

  • For String algae and Planktonic algae: Use AlgaeLift for all types of algae. Click the link for specific application instructions.

5. Algaecides

Overview:

Algaecides definitely kill blooming algae. You’ll often even see instant results. In this way, they can be effective at reducing algae, however, they do nothing in the way of getting rid of the problem for good. 

  • The limits of algaecides: Firstly, algaecides rarely kill algae seeds and spores. These seeds/spores often lie dormant in your dam until favourable conditions return. And secondly, algaecides in no way clean up the algae once it’s dead. This dead material eventually decays, adding more nutrients to your dam that can feed future algal blooms.
  • Pro tip: If you really must use algaecide, we recommend using a product like Biostim Accelerator at the same time, for faster and better long-term results. Biostim Accelerator is a 100% natural biocatalyst (made of bacterial cultures, enzymes, fungi and stimulants) that accelerates the effectiveness of algaecides and herbicides. Like methods 1 and 2, the concentrate encourages the growth of naturally occurring bacteria, which (i) breakdown the dead algae before it turns to fertiliser, and (ii) deplete nutrients in your dam, making conditions unfavourable for algae seeds and spores. Biostim Accelerator is also effective in breaking down the hard-to-penetrate slime layer that forms on algae. This means the algaecide can get into contact with the algae faster and with less chemical needed, a win for both mother nature and your wallet. 
  • Beware of copper-based algaecides: If you’re using a copper-based algaecide, it’s worth knowing that once the copper is in your aquatic system, it never leaves. So, if you keep applying more and more, it will build up. Typically, this copper remains dormant, but under certain conditions it’s been known to release into dams all at once causing mass fish kills. This isn’t a common occurrence, but it does happen. This is why we don’t recommend copper-based algaecides be used often. And certainly, beware of any supplier who tells you to use a copper-based algaecide as a preventative or ongoing treatment.
  • Never use copper sulphate algaecides: You’ll rarely find copper sulphate algaecides on the shelf today. It’s actually illegal in most places in Australia. And for good reason, it kills all life; everything. It was a poor recommendation made to farmers back in the day. Now, it’s largely gone from the market, but there are still the odd cases of people using it, mainly because a tiny few rural ag stores (who are clearly poorly informed) continue to sell it, and therefore tell people to use it.

Application:

7. Ultrasonic sound

Overview:

An ultrasonic algae treatment involves having a device in the water that sends out ultrasonic waves which can travel massive distances, often acres of water. It’s a similar effect to the stereotype of the opera singer shattering glass with just the right note. Different frequencies can be used against different algae. The problem with ultrasonic treatment is it’s not effective at killing every type of algae and, as discussed above, the method does nothing in the way of tackling the cause of your algae problem, i.e. nutrients.

Application:

  • String algae: Not recommended as it’s not very effective against string algae.
  • Planktonic algae: Ultrasonic treatments are best suited to planktonic algae and cyanobacteria. We recommend you: (i) first have your algae identified so you can check if it’s on the manufacturer’s list of species impacted by the frequency of the device, or (ii) make sure the product you use has a large range of frequencies to maximise your chance of success.  

7. Manual removal

Overview

Manual removal using rakes and nets is not as silly as it sounds, especially if you’re having a problem with string algae. Our advice would be to pair manual removal with either aeration or a probiotic treatment. By manually removing as much algae as you can, you’ll radically increase the speed of your results because there is far less material for the aerobic bacteria to starve out and break down. 

Application

  • String algae: We recommend using an aquatic rake or net, or if the fronds are larger enough, you could even try pulling them out by hand.
  • Planktonic algae: Not recommended. You could try a very fine net, but even then, you’re only likely to catch large algal cells.

Bad ways to attack algae

The final methods are bad ways of combating algae because they don’t focus on the cause of the problem, and their results are mild at best.

8. Barley straw

Overview

The idea with barley straw is you put bales of straw in your dam. As the bales decay, they release small amounts of hydrogen peroxide. Unfortunately, the idea is an old wise tale, or perhaps an unwise tale. The method is rarely effective because the straw doesn’t release anywhere near enough hydrogen peroxide to put a dent in a decent sized algal bloom. You’d be better off using something like AlgaeLift—it’s the same idea but far more potent.

You could argue with enough straw bales you’d reach a decent level of hydrogen peroxide to impact the algae, but it’s unlikely to be economically or manually feasible. Especially when you must get the bales back out of the water before they decay. Otherwise, you’ll achieve the opposite effect, they’ll become fertiliser for algae. And no one wants to pull a heavy, soggy, half-rotten bale of straw out of their dam. Especially not for subpar results.

It’s worth noting, you can buy barley straw in a liquid form, but this is just water taken from rotting bales and bottled for sale. Your guess is as good as ours as to how potent (or not) each bottle is but even the most potent barley straw liquid won’t get close to AlgaeLift.

Application:

  • We don’t recommend this method for any type of algae. 

9. Fish 

Overview:

Fish may be somewhat helpful with eating some string/filamentous algae, but not planktonic algae. Overseas, the best fish at eating algae is tilapia, although they are illegal in Australia. Here, silver perch are your best bet. They’re a good species to choose in general because they are omnivores, making them one of the easiest fish to keep alive. The big caveat here is there is a big question mark over how well your fish will actually attack your algae—they’re just as likely to feed on the bugs and other life in your dam and leave the algae alone. That said, if you do have fish and want to try it, keep your expectations reasonable.

Application:

  • String algae: Fish may eat string algae if you: (i) don’t feed them, so they are hungry, and (ii) have them stocked in high numbers, so food is limited.
  • Planktonic algae: DO NOT introduce fish.

10. Carbon/UV/Ozone filtration 

Overview:

Carbon, UV and ozone filtration are great for algae reduction in fish tanks and small ponds, but not dams. There are options out there, but they are far too expensive and impractical for the average residential dam owner.

Application:

  • We don’t recommend this method for any type of algae. 

Need advice? Complete our Dam Diagnostics Survey and we’ll be in touch. Scotty Tucker offers free, no-obligation advice.