Agriculture News: Pond algae bloom can be a serious situation

By Keenan Bishop, Published:

I’m sure most have heard by now of Toledo’s recent ban on drinking water from Lake Erie. This time of year I usually get a few questions about bright green or even red algae on farm ponds. The question is not about the safety of humans consuming the pond water but obviously the livestock. The issues in Toledo, however, show how serious this can be.

Algae occur naturally in bodies of water. It usually only becomes an issue when it “blooms” or experiences a big growth or concentration because of weather conditions. Hot, dry weather can cause this especially when combined with chemical fertilizer runoff or animal manure. Winds can also concentrate the algae by blowing it into one corner or side of the lake or pond.

According to the EPA ( the most commonly occurring groups of freshwater algae are diatoms, green algae, and blue-green algae, which are more correctly known as cyanobacteria.

Cyanobacteria refer to a group of microorganisms that possess characteristics of algae (chlorophyll-a and oxygenic photosynthesis). They are found in fresh, estuarine, and marine waters in the U.S. Cyanobacteria are often confused with filamentous green algae, because both can produce dense mats that can impede activities like swimming and fishing, and may cause odor problems and oxygen depletion; however, unlike cyanobacteria, filamentous algae are not generally thought to produce toxins.

Most of these blooms we see are blue-green algae. There are over 2000 species but less than one hundred are poisonous.

Cyanotoxins can be produced by a wide variety of planktonic (i.e. free living in the water column) cyanobacteria. Some of the most commonly occurring genera are Microcystis, Anabaena, and Planktothrix (Oscillatoria).

Almost always toxic

Microcystis is the most common bloom-forming genus, and is almost always toxic. Microcystis blooms resemble a greenish, thick, paint-like (sometimes granular) material that accumulates along shores. Scums that dry on the shores of lakes may contain high concentrations of microcystin for several months, allowing toxins to dissolve in the water even when the cells are no longer alive or after a recently collapsed bloom.

The blue-green algae toxins are released when the cells are damaged and die. This could happen when treating pond with copper or inside the animal’s digestive tract after ingesting. In humans it can cause rashes, mouth and throat irritation, and nausea.

Animals can seem weak, stagger, slobber, have trouble breathing and even die. Some algae produce liver toxins. Animals are most at risk when drinking from a water source during a bloom or cleaning their coat or fur after exiting the body of water.

Many are harmless

Many blooms here are from the harmless green algae but visually you can’t really tell the difference. The UK Veterinary Diagnostic Lab ( will accept samples for testing and forward them on but the cost is almost $225 (still way cheaper than a dead calf or cow). Another problem is that there are many blue-green algae toxins for which there is no test.

The best thing to do is provide a cool clean source of water for livestock and fence them out of streams and ponds. Free flowing water can probably be considered safe but if they have access then they can contaminate it with their feces and urine and cause problems downstream. If you treat a pond with copper wait at least a week before allowing drinking access.

In the grand scheme of things, the best solution is for homeowners and farmers to reduce or even eliminate fertilizers (and pesticides) from running off into the storm drains and streams and ultimately into our water sources and feeding the blooms. Farmers are already encouraged to fence animals out of streams and other water sources.

By the way, if you haven’t created or updated your Water Quality Plan ( then maybe now is a good time to do so. The time it takes to do it is a lot cheaper than a fine.

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