Watch for deadly blue-green algae blooms in ponds and watering sites

The algae is actually a photosynthetic bacteria that thrives with warm weather, 
calm winds and abundant nutrients, particularly phosphorus and nitrogen

Livestock producers should watch for green to blue-green scum in fresh water supplies.

“Algae blooms cause major disruptions, not only because of their offensive odour and appearance; but because they can be fatal to livestock, pets and people,” says Roxanne Johnson, a water quality associate with North Dakota State University’s extension service.

“Not all algae blooms are toxic, but without laboratory analysis, it is impossible to identify poisonous species.”

This seasonal event is not really algae but a photosynthetic bacteria called cyanobacteria, which thrive with warm weather, calm winds and abundant nutrients, particularly phosphorus and nitrogen.

A “bloom” of green or blue-green algae on the surface of the water can appear overnight and be accompanied by an unmistakable musty, earthy or putrid odour.

“As cyanobacteria break down, they release toxins that can be an irritant to human skin and potentially lethal to animals,” says Johnson.

Concentrations of algae develop as the wind moves the toxin to the leeward, or downwind, shore, where you may find evidence of toxicity, such as dead mice.

Blue-green algae produce two toxins, each with different symptoms.

Signs of neurotoxin poisoning usually appear 15 to 20 minutes after ingestion. In animals, symptoms include weakness, staggering, difficulty in breathing, convulsions and ultimately death. In humans, symptoms may include numbness of the lips, tingling in fingers and toes, and dizziness.

Signs of liver poisoning may take hours or days to appear. Liver toxins can cause abdominal pain, diarrhea and vomiting in humans and death in animals.

Most blooms are obvious to the naked eye. However, blue-green algae can be present in water without a visible bloom, says Johnson.

She advises livestock producers to treat their water if they’ve had blooms. Treatments include using an aeration/mixing device to create turbulence in the water and minimizing nutrient levels by establishing vegetated buffer strips around the water to intercept and trap nutrients and sediments.

Fencing ponds and pumping water to a tank or trough in order to keep livestock from trampling the area reduces the risk of blooms. Tanks need to be cleaned on an annual basis to minimize algae growth.

Some producers are adding dyes, such as Aquashade, Blue Lagoon and Admiral, to non-flowing pond water to filter out ultraviolet rays. According to the products’ labels, this treatment is most effective when used early in the season in water intended for livestock consumption. It is not recommended for human drinking water.

Algaecides, such as copper sulphate, are effective in killing algae blooms, but also can kill fish and damage the ecosystem of inland waters, Johnson says. Lethal levels of toxins may result as a consequence of algae cell walls rupturing when copper sulfate is used.

“While there are no quick fixes to control blue-green algae once they appear, reducing the amount of nutrients washed into ponds may eventually lessen the intensity of the bloom,” Johnson says.

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