How to Get Rid of Sludge from a Dam—Guaranteed Results

Having a problem with sludge on the floor of your dam? The squishy, muddy feeling between your toes that tends to smell. The good news is you can get rid of sludge, and you can achieve this without adding a single chemical to your water. Follow the steps below and you can expect to see your sludge drop by 5-10cm a month. 

First, let us look at what sludge is.  

What is sludge? 

Sludge is generally composed of water (around 70%) and organic and inorganic material (around 30%). This organic material is typically made up of dead bacteria, decomposing plants, animal faeces (e.g., duck and fish poo), seeds of aquatic weeds, and the dormant cells of algae (called “akinetes”), which are waiting for the right conditions to spring to life. Inorganic material is soil and dirt.  

The reason sludge tends to smell is because as the layers begin to pile up, oxygen is unable to penetrate the substrate. This turns the material anaerobic, which promotes the growth of anaerobic bacteria (i.e., bacteria that function “without oxygen”). Anaerobic bacteria produce toxic gases such as methane and hydrogen sulphide—hence the smell.  

How to get rid of sludge 

The key to getting rid of sludge is to change the conditions in your dam so aerobic (“oxygen loving”) bacteria replace the anaerobic (“oxygen hating”) bacteria. Not only do aerobic bacteria not produce bad smells but they are also much more efficient at breaking down organic material. In other words, aerobic bacteria feed on decaying material at a much faster rate—breaking down the layers of sludge.  

Aerobic bacteria also consume nutrients such as nitrogen and phosphorus that living pests (e.g., aquatic weeds and algae) depend on for survival. This means, as well as consuming the dead material, aerobic bacteria reduce the rate at which living material can grow. So, over time, less dead material accumulates on the floor of your dam.  

Okay, so you need to change your dam conditions from anaerobic to aerobic. How do you do this? 

Step 1: Increase oxygen levels in your water with an aerator 

First, you need to add more oxygen to your water so anaerobic bacteria starve and aerobic bacteria thrive. This is done by aerating your water using an aerator. There are two types of aerators: surface aerators (which operate above the water) and sub-surface aerators (which operate below the water, on your dam floor). 

Surface aerators

Surface aerators work by pumping water up out of your dam in a fountain-like display. The water shoots up into the air, which cools and bonds with oxygen in the atmosphere before falling back down to the surface of your water. This cooler “oxygenated” water is denser and less buoyant than the water in your dam and therefore sinks to the bottom. This sinking water pushes less oxygenated water sitting at the bottom of your dam to the surface which is then pumped through the aerator (and the process is repeated). Over time, more and more oxygen is added to your waterbody.

Here are some example surface aerators we stock:

Air-O-Lator Carnival Aerating Fountain
  • Dam size: ½ to 2.5 surface acres
  • Depth: 0.5 to 5m
  • Solar available: Yes

Watch video

Air-O-Lator Professional Aerator
  • Dam size: ½ to 1 surface acre
  • Depth: 0.5 to 5m
  • Solar available: Yes

Watch video

Air-O-Lator Commercial Aerator
  • Ideal for wastewater lagoons
  • Depth: 0.5 to 5m
  • Solar available: Yes

Watch video

Sub-surface aerators

Sub-surface aerators work by pumping air up from the floor of your dam through diffusers/air-stations. This air rises to the surface with the bubbles getting larger and larger the more distance travelled. This creates a wake which draws water from the bottom of your dam up to the top, like riding a bike behind a bus and not needing to peddle because you are being dragged along by the sucking air. These bottom waters arrive at the surface and gas exchange occurs between the water and the air. Here, nasty gases like carbon monoxide, methane and hydrogen sulphide exit the water while oxygen enters the water. Through this gas exchange, the water cools and gets denser, again sinking. This takes oxygen down to the lower parts of your dam, which pushes bottom waters up, and the cycle repeats itself. 

Here are some example sub-surface aerators we stock:

Hakko Lineal Diaphragm Aerator
  • Dam size: up to 1 surface acre
  • Depth: 0.5 to 2m
  • Solar available: No

Watch video

Matala Rocking Piston Aerator
  • Dam size: ¼ to 4 surface acres
  • Depth: 1.5 to 12m
  • Solar available: Yes

Watch video

Vertex Rocking Piston Aerator
  • Dam size: ½ to 20+ surface acres
  • Depth: 1.5 to 12m
  • Solar available: Yes

Watch video

OWS Windmill Aerator
  • Dam size: up to 2 surface acres
  • Depth: 1.5 to 9m

Watch video

Step 2: Accelerate the growth of aerobic bacteria with a probiotic 

Now that you have the right conditions for aerobic bacteria to grow (with an aerator in place) you can speed up the rate at which this growth happens by feeding your bacteria probiotics. Much like you eat Greek yogurt or drink kombucha to feed the beneficial bacteria in your gut, these probiotics feed the aerobic bacteria in your dam so they can grow in number.  

We recommend Biostim pellets or tablets as a probiotic (brochure link below). Biostim is our own label of 100% natural probiotics. They contain naturally occurring bacterial cultures, enzymes and stimulants which promote the growth of aerobic bacteria.  

Note: we also offer Biostim liquid and powder, which contains similar ingredients, however, this is less likely to sink to the bottom and embed in the sludge. Liquid and powder are better for floating debris. For sludge, we recommend Biostim pellets or tablets (these are essentially the same product; however, tablets are more concentrated than pellets and therefore work faster). 

Results: 5-10cm reduction in sludge per month 

The result of these two forces encourages more and more aerobic bacteria to grow. These guys compete with anaerobic bacteria for resources (e.g., nitrogen and phosphorus) starving out the anaerobic bacteria which are already suffering in the oxygenated water.  

As mentioned above, aerobic bacteria also feed on the organic material in the sludge itself (e.g., dead leaves, duck poo, aquatic weed seeds, algae spores) breaking it down, so it begins to disappear altogether. It is important to note that anaerobic bacteria also feed on sludge but at a much slower rate, often at a rate that is slower than the speed at which the organic material is piling up. 

As mentioned at the top of this article, you can expect to see a reduction in your sludge by 5-10 cm per month when recommended dosage rates for Biostim are followed assuming your water is well aerated and mixed. Exact results will depend on sludge composition and water temperature. 

More benefits… less algae and weeds 

Another massive benefit of reducing sludge is that you will greatly reduce the chances of algae and aquatic weeds growing in your dam too. This is because the sludge on the floor of your dam is essentially a fertiliser that feeds these unwanted pests. Less fertiliser means less algae and weeds, which as well as less unwanted pests, means less material in your water that eventually dies off and sinks to the bottom, becoming sludge. So, a win, win, win. 

Want help? 

Get customised advice on reducing sludge in your dam 

Scotty Tucker, our Managing Director with 20+ years’ experience in improving water quality, can provide you with free, no-obligation recommendations. Simply fill in our Dam Diagnostics Form and we’ll be in touch.