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Diagnosing Your Pond: Colour, Algae, Weeds

Diagnosing Your Pond: Colour, Algae, Weeds

Our team likes to run through a standard set of questions including presence of algae and type, presence of weeds and type, “muck,” and colour and consistency of water. These factors guide our treatment protocols. You can also check these out yourself using our Pond Pro Diagnostic Tool.

Maybe you have observed what your pond’s conditions are - but what does all this mean? The presence of plants and the colour of the water are all indicators of overall pond health. While this topic is too extensive to cover everything, we will break down the most common issues:

Water colour/consistency:


Cause: Algae signals that there is nutrient overload, and is very common in older and untreated ponds or a result of fish waste or other waste buildup, fertilizer run off, manure run off, leaf litter deposits, and more. Aquatic plants are not actually a concern in this case, and in fact, they can provide essential oxygenation to your pond and reduce water colouration. It is when these plants die and rot (especially in late season) that they add ammonia and nitrate to the water contributing to the “green” look.

Actions: Nutrient load can be reduced by adding bacteria to your pond that break down these nutrients, or by providing aeration, that will support natural populations of aerobic bacteria. Other tips:

  • Do not overfeed your fish. This leaves behind residual nutrient-loaded pellets.
  • Sunlight assists photosynthesis of algae. To reduce this affect you may want to invest in plant cover (e.g. waterlilies), pond dye, or a UV sterilizer.


Cause: Foamy water is more common in water that is used for fish, as a result of protein from decaying organics. This foam is not always a problem and it may resolve on its own, but excessive amounts of it can become worrisome; this is when it can block natural gas transfer and harm aquatic life.

Actions: Foam can be a result of water and oxygen mixing in a water current, but to be safe on the safe side, we always recommend testing other causes (e.g. high ammonia and nitrates).


Cause: Water may be brown from organics or clay. We have a separate post that investigates “murky” water, a result of high turbidity.

Actions: Organic turbidity (from decaying matter and debris) is treated with flocculents and inorganic turbidity (from clays and soils) is treated with floc logs. Brown water may be reoccurring if the organic matter forms a sludge layer on the bottom of the pond. If you are experiencing brown water with persistent muck, the suggested course of treatment is first to apply flocculent (binding free-floating phosphates to the bottom) and then to follow up with a course of muck pellets 1-2 days later (bottom-dwelling bacteria that consumes nutrients). If you are unsure about the cause of your discolored and brown water, we strongly recommend that you get your water tested. Pond Pro offers water testing services, conducted by our biologists, to look at basic parameters which may contribute to turbidity concerns. We can also test your water against various water treatment products to determine which product is right for you at a custom-determined rate!


Filamentous Algae:

Cause: As a result of excessive nutrients (particularly nitrogen and phosphate) this filamentous algae forms dense mats. This algae starts growing from the bottom of the pond, but as it photosynthesizes it traps air bubbles in its mats which causes it to rise. As the weather warms up and we are experiencing more sunlight, algae can emerge from the deep very suddenly. An overgrowth of algae can result in fish kills (algae consumes oxygen at night and as it slowly decays).

Actions: We recommend using a rapid treatment of Proclear Algaecide and follow with a treatment of bacteria to break down dead algae before it contributes to nutrient overload. If algae slime is covering rocky surfaces, we recommend using the product Slime Away. For specific information on treatment protocols regarding algae check out our blog post here.

Blue-green/Planktonic (cyanobacteria):

Cause: This algae is a result of nutrient overload (particularly phosphorus and nitrogen). Consider sources such as agricultural and stormpwater run-off or septic system leaching. Blue-green algae can produce toxins that are hazardous to human health and pets. There are a few ways you can distinguish it from filamentous algae, including by the “stick test” - putting a stick in the water, and if it is blue-green algae, it will not attach. Blue-green algae is described as having the appearance of “grass clippings” or “pea soup.”

Actions: Dependent on regulations in your area. Contact your municipality to discuss next steps. 

Aquatic Plants: 

Surface weeds (Duckweed):a result of nutrient-rich water. It can be a result of a build-up of debris on the bottom of your pond. It is also more common in slow moving or stagnant water. Check out our blog were we talk about duckweed management here.

Submerged weeds: are not necessarily a problem - they contribute oxygen, improve water quality, provide nutrient storage, fish cover, and a wildlife food source. According to Fisheries Specialist D. Allen Pattilo, 15-25% of water’s surface area should contain submerged plants to support fish.

However, when they become a nuisance or are grow excessively in dock/swimming areas, weed rakers and circulators can help manage them. 

More questions? We'd love to hear from you! Please contact us at

8th Mar 2024 Pond Pro Canada

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