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Blue-Green Algae Is A Killer

Blue-green algae in dugout water can be fatal to cattle, but it’s not always easy to spot. The worst-looking algae-laced dugouts may pose no risk while a relatively clear dugout just down the road could be a killer.

Algae may be undesirable but somewhat inevitable in a dugout,” says Paul Prodahl, conservation technician with Ag. Canada’s agri-environmental services branch (AES) at Rosetown, Sask. “If algae are the green or brown types, they’re probably not the cause of health problems in livestock, though they do degrade the quality of the water. Blue-green algae are completely different.”

The name is a misnomer since the blue-green organism is actually a type of bacteria, cyanobacteria, rather than an algae. Cyanobacteria are unique among bacteria in that they contain chlorophyll and use the sun as an energy source.

Algae and cynobacteria occur naturally in surface water. They may not be visible to the naked eye until they go into rapid reproduction and cling together to form clumps known as a bloom.

While algal blooms are never toxic to people and animals, some types of cyanobacterial blooms can produce lethal liver toxins or neurotoxins when they begin to die. However, you can’t tell if the bloom is producing toxins just by looking at it.

Typically, livestock poisonings occur when the wind blows the dying bloom into a concentrated mass at the edge where cattle drink.

There’s no sure way short of a lab test to identify what types of algae and cyanobacteria are in your dugout, just as there’s no sure way to predict whether a bloom will occur.

Blooms are most likely to form in warm, standing or slow-moving water. They also require light, oxygen and nutrients, therefore, they are more likely to occur when nutrient levels (particularly phosphorous) in the water are high. Cyanobacterial blooms are mostly associated with standing water and may or may not occur with algal growths.

Just because you’ve never had or noticed cynobacterial bloom in your dugout is no assurance that it will never happen. The organisim can be transported from one water source to another by birds, animals, or on dry soil picked up by the wind.

Your nearest AES branch or provincial agriculture office will have people who can assist or advise you about the possibility of sending samples to a lab for testing.

How to tell them apart

Prodahl says once the blue-green bloom of cyanobacteria is thick enough it’s unmistakable. It looks like a shiny, reflective slick floating on top of the water. The clumps will break apart easily when you swish your hand through them. Heavy blooms have been described as looking like pea soup.

There’s a simple way to make a quick assessment as to whether the bloom is the filamentous type typical of algae, or the planktonic type typical of cyanobacteria. Scoop some of the bloom out of the water. If long, stringy material is left hanging from your fingers, then it’s the filamentous, nonpoisonous bloom of green or brown algae. None of the toxic cyanobacteria produce this type of bloom. If all that’s left are bits of green particles sticking to your slimy-feeling hand, it’s likely a planktonic bloom and most likely from cynobacteria. Some of the harmless green and brown algae produce planktonic blooms as well.

If it’s a planktonic bloom, be on the safe side — assume it’s toxic and keep livestock away from the dugout.

Duckweed is a beneficial aquatic plant that is sometimes confused with the planktonic bloom of cyanobacteria. The tiny individual plants sometimes cover the entire surface of the pond, particularly if it is sheltered from the wind. Duckweed is distinguishable by its hair-like white root that hangs from the underside of

the plant into the water. The roots remove nutrients from the water and the plant mass blocks out light, thereby limiting two factors associated with inducing algal and cyanobacterial blooms.

The key to managing duckweed is to remove as much of it as possible before it dies and sinks to the bottom of the dugout later in the season, Prodahl adds. Decomposition uses up a lot of the dissolved oxygen in the water, contributing to the non-aerobic decomposition process that causes the horrible rotten-egg odour.

Treating a bloom

“If you suspect the bloom is from cyanobacteria be proactive in treating it — the sooner the better,” Prodahl says.

Copper sulphate (bluestone) is the most common treatment. It effectively kills cyanobacteria when applied in very low doses, however, it’s not realistic to use copper sulphate to try to keep a dugout free from algae. It shouldn’t be used as regular preventative maintenance because it can kill other beneficial organism in the dugout, and cyanobacteria and algae can build up a resistance to it, he advises.

Copper sulphate products are available in granular and liquid form. The concentration of the active ingredient (copper) ranges from five to 25 per cent by weight. Your target dose should be 0.25 mg Cu/L of water in the top one meter of the water body. Reduce the rate by 60 per cent if you’ve stocked the dugout with fish.

The old practice of placing dry copper sulphate in a nylon socking, tying ropes to both ends of the nylon, and having two people drag the sock back and forth along the top of the water is still a recommended method of application. Alternatively, you can dissolve dry products in water and spray the solution over the surface of the water as you would when using a liquid product.

Spot spraying may be all that’s necessary if you catch the problem early or the bloom is concentrated in one area of the dugout. Add one teaspoon of dry copper per gallon of water in the sprayer.

Remember, treating a cyanobacterial bloom with copper sulphate will cause the cells to burst and release toxins into the water. People and animals should avoid drinking the water for at least two weeks following treatment to allow time for the toxins to degrade.


It’s more difficult to fix problems than to prevent them.

Prodahl says aeration will give you the biggest bang for your water treatment buck. It will keep water moving and help to prevent the layer of warm water at the top where blooms occur. It’s important to use a diffuser to create tiny bubbles of oxygen that dissolve in the water. You don’t want to see big bubbles breaking the surface. There are solar-powered and wind-powered aeration systems that are decent alternatives to electric pumps for use in remote locations, he adds.

Prevent, or limit as far as possible, the amount of nutrients entering the dugout from agricultural lands and livestock activities. Nitrogen and phosphorous are great fertilizers for algae, too. Sediment in runoff water and excrement from livestock entering the dugout to drink are the methods for these nutrients to get into the dugout, Prodahl explains.

Research shows that the first flush of runoff in the spring carries the highest concentration of undesirable nutrients. If you’re in an area that has lots of runoff, you might have the luxury of letting the first water go by. Once the dugout is full, it’s important to route excess runoff around the dugout. If water continues to flow through, it will slow down as it enters the full dugout and lose its ability to keep sediment in solution.

“Any time you are considering making a hole for watering livestock, it’s important to know ahead of time how it’s going to fill. There are lots of construction techniques you can use when making a dugout or pond to help give control over the water that comes in,” Prodahl says. If you’re past the construction stage, you still have many options for designing physical features to manage water flow. Simple measures, such as grassing buffer strips and waterways, are very effective ways to trap sediment before it gets to the dugout.

Call Paul Prodahl at 306-882-5678 for more information or go to AAFC’s website at,click the land managers tab on the left and look for the water supply and quality section.

— Debbie Furber

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