Your Reading List

Blue-Green Algae Poisoning


Having practised in Western Canada for over 25 years I have yet to diagnose a known case of algae poisoning. In Eastern Canada, with the growing human and livestock populations surrounding water bodies, there have been increasing problems, and it may only be a matter of time before the incidence increases out west.

With recent flooding and excessive moisture, phosphorus and nitrogen increases in dugouts and lakes, increasing algal blooms. There are some permanent and temporary preventive measures we can do to decrease the incidence.

Generally, algae poisoning is very acute, causing sudden death in an outbreak form where several head are involved. Blue-green algae, also known as pond scum, will cause the water to look like blue-green soup in a dense bloom with solid-looking chunks in it. Fresh blooms smell like grass clippings whereas old blooms smell like rotting garbage. Winds can concentrate the blooms on one side of a water body but the toxins produced by the algae can dissipate in several days in the water, making diagnosis difficult.

The death of the algae by cold weather, winds or rainfall is what releases the toxins into the water. We get most algal blooms in late summer and early fall. Clinical signs most commonly involve several animals with sudden death being the common denominator. If seen alive, nervous symptoms predominate since the toxin affects nerve transmission. Death is caused from respiratory failure.


If the animal survives, liver damage and photosensitization (sunburn) predominate. Most often clinical signs would start within 15 minutes of consuming water, so affected animals are often found down or dead not far from the water source.

These blooms are caused by ever-increasing amounts of nutrients such as phosphorus and nitrogen derived from animal and human wastes. Manure and urine from animals or human septic systems as well as crop or lawn sprays lead to these increasing nutrients in our water level. Wildlife are not immune to this poisoning and are often the sentinel animals. Any time dead deer, moose etc. are seen close to a water supply suspicions should be raised.

Even human skin contact with the affected algae or water will lead to rashes, eye irritation and abdominal cramps. In some jurisdictions mandatory vegetation buffer str ips around lakes minimizes runoff and sediment which lead to the algal blooms and potential poisonings by wildlife, domestic livestock, birds or humans. The toxin can even be passed up the food chain when predatory birds eat small birds poisoned by the algae.

Minimizing the manure, sewage and fertilizer getting into our water sources should keep these algae in check. The government is controlling the amounts of phosphorus in washing detergents, another identified contaminant of our water supply.


Several things are now commonly done at the farm level and greatly minimize this contamination. Spreading manure at the right times and not on top of snow minimizes the likelihood of contamination at spring runoff. Not feeding cattle close to waterways or drainage areas also minimizes this risk. These same practices help minimize the likelihood of contamination with E. coli O157: H7, another potentially deadly human bacteria.

The controlled exposure of cattle to open water by using solar-powered pumps, nose pumps, wells or other methods to supply water decreases contaminat ion from defecation in the water. It has been proven they also have better performance when drinking cleaner water.

Movement of animals in the water, or boats in shallow lakes stir up the bottom bringing up the phosphorus and nitrogen and aggravating the problem. If you can’t completely fence the water areas, the second-best alternative is to have fresh water in a tank. Animals will choose the easiest route. The water intakes for these systems are placed way below the water surface away from the algal toxins, thus making the water much safer.

If you do get algal blooms where any livestock have access, they can be controlled by using copper sulfate in the water. Amounts of as little as 1/4 to 1/2 lb of copper sulphate per 100,000 gallons will do the trick. The toxins may dissipate in as little as five days but the recommended time frame is three weeks after treatment before access is allowed.

A simple way to calculate the copper sulphate necessary is to pace off the dugout length and width. If you know or can estimate the average depth figure out the total cubic feet. One cubic foot is 6.24 gallons so multiplying the cubic feet by 6.24 will give you the total. Most large dugouts only need one or two pounds so is a very inexpensive way to get the job done. I have the producers dissolve the copper sulphate in a stock solution so it can be spread around and equally distributed.


By monitoring and protecting your water supply cattle diseases such as algae poisoning, coccidiosis or human diseases such as e coli will be greatly reduced. The livestock will do better and environmentally riparian areas are preserved with wildlife being better off. Visually and by the smell most times you should be able to spot algal blooms. Keeping check will make us all better stewards of the land for future generations.


Anytimedeaddeer, moose,etc.areseen closetoawater supply,suspicions shouldberaised.



Stories from our other publications