Blue-green algae, which typically looks like a pea-green “cover” on the surface of farm ponds, is a hot, dry weather threat to livestock, people and pets. The Wisconsin Department of Natural Resources is warning that record-setting temperatures are contributing to blue-green algae blooms; the DNR is urging caution during water-based recreation, sport-dog training or pet exercise. Farmers need to find alternative fresh-water sources to low-ponds for their cattle, sheep, horses and other farm animals.
Blue-green algae (technically known as cyanobacteria) aren’t the type that can be picked up as clumps, but disperse easily in the water if disturbed. As this algae dies, it releases toxins in the water. Dairy and beef cattle and other livestock shouldn’t be using pond water this summer, warns Mena Hautau, a Penn State University Extension educator. Algae blooms are often an indicator that a pond has too many nutrients. When pond water becomes stagnant late summer, has a warm temperature and has lots of available nutrients (like phosphorus), algae growth can be excessive – and the poisoning threat blooms. It should be noted that other non-health-threatening algae can also bloom at nuisance levels and may be mistaken for blue-green algae.
“Reports of health concerns due to exposure to toxins produced by some blue-green algae are growing after our recent hot weather,” says DNR aquatic research scientist Gina LaLiberte. “People should be on the lookout for water with a green ‘pea soup’ appearance - or which contains green, blue, white, red, or brown scum that may be foamy or in mats or blobs. If you have any doubts about the appearance of water, you should stay out.”
Swimming, even wading, should be avoided in ponds and areas of lakes and rivers where a scum or mat of algae is present; washing off after swimming in any lake, pond or river also can be helpful. The most commonly reported symptoms of exposure to blue-green algae blooms in humans include rashes, gastrointestinal ailments (with ingestion), and respiratory irritation, according to Mark Werner, a toxicologist with the Wisconsin Department of Health Services.
Children may be at greater risk than adults for two primary reasons. They love to play in the water, but typically don’t understand the health risks as well as adults. As a result, they may drink the water because they are thirsty or swallow it accidentally while swimming. Second, children weigh less, and so a smaller quantity of toxin may trigger an adverse effect.
People experiencing symptoms that may be due to blue-green algal exposure (i.e. stomach cramps, diarrhea, vomiting, headache, fever muscle weakness, difficulty breathing) should immediately contact a doctor or the Poison Control Center at 800-222-1222. They’re also encouraged to report potential algae-related illnesses to the Wisconsin Department of Health Services (608-266-1120).
If your farm or hunting dog, barn cat or cattle display symptoms such as abnormal sluggishness, seizures, vomiting, or diarrhea after contact with surface water, contact your veterinarian right away. Dogs are particularly susceptible to blue-green algal poisoning because scum can attach to their coats and be swallowed during self-cleaning.
“Animals have a higher risk from dying after exposure to blue-green algae toxins because they may ingest large amounts of toxins from drinking lake, pond, or river water or licking algae from their fur,” warns DNR veterinarian Lindsey Long.
The DNR warns that some algal species produce toxins that, when ingested, can harm neurological systems or the liver of people, pets, livestock and wildlife. Not all cyanobacteria produce toxins, but the presence of blue-green algae blooms is an indication that the public can use to determine a potential hazard. Farm families need to be aware that this phenomenon can kill – livestock and people – due to neurotoxins and hepatotoxins.
Livestock poisoned by a blue-green algae bloom typically live less than 24 hours. Death may be preceded by muscle tremors and “paddling.” Diarrhea might also be seen. There might also be a greenish algal stain on their mouth, nose, legs and feet. Cattle and horses that survive acute poisoning may suffer from photosensitization in areas particularly exposed to sunlight (i.e. nose, ears and back), followed by hair loss and skin sloughing. There’s no effective treatment for this poisoning. Affected livestock are usually found sick or dead near the pond.
According to Iowa State University, algae blooms can be stimulated following storms or heavy rainfall, when surface runoff containing phosphorus and nitrogen enters the water. The blooms can be quite bad when storm events are followed by prolonged periods of hot temperatures.
DNR reports that when environmental conditions are just right, blue-green algae can grow very quickly. Most species are buoyant and will float to the surface, where they form “scum” layers or floating mats. In Wisconsin, blue-green algae blooms generally occur mid-June to late September, although in rare instances, blooms have been observed in winter, even under the ice.
By design, many farm ponds are constructed to trap nutrients and eroded soil. Because more nutrients may be available and these types of ponds are generally more shallow and warm, it is possible for them to experience more frequent blue-green algae blooms (which may produce toxins). Again, a common sense approach is recommended for such ponds: if a scum layer or floating mat is present, don’t let livestock have any access. The same goes for your children and stock dog.
Steve Ensley, ISU veterinary diagnostic and production animal medicine clinician and Chris Filstrup in ISU’s llimnology lab, warn that because it’s difficult to predict toxicity from these algal blooms, it’s best to not let animals drink, or in the case of dogs, swim, in water that’s “pea soup” green. Occasionally, livestock are found dead next to water with blue-green algae blooms. Clinical signs of neurotoxin poisoning are rapid onset of rigidity and muscle tremors followed by paralysis, cyanosis and death.
As noted, blue-green algae also can produce hepatotoxins (that are toxic but do not kill livestock as rapidly as neurotoxins). Clinical signs associated with hepatotoxins include gastrointestinal tract disturbances characterized by vomiting (depending on species), abdominal pain and diarrhea. Often, severe hemorrhaging into the liver can cause shock and death. If death due to shock doesn’t occur, then death results from liver failure, often within 24 hours. Secondary (“hepatogenous”) photo-sensitization can occur after ingestion. On autopsy, the liver often is enlarged, swollen and dark red. Contact your veterinarian if you suspect blue-green algae poisoning.
DNR cautions that even if you can’t see blue-green algae floating on the surface of the water, that doesn’t mean they aren’t there. Blue-green algae can be suspended at various depths in the water, and their location depends on a number of factors. The most important of these are light and nutrients (phosphorus and nitrogen). Many species of blue-green algae are able to control their buoyancy as the availability of light and nutrients change with the time of day and local weather conditions. At night, when there is no light, cells are unable to adjust their buoyancy and often float to the surface, forming a surface scum. So this scum can literally appear overnight and may linger until wind and waves scatter the cells throughout the water body.
Chemical treatment of a pond experiencing a blue-green algae bloom may kill the blue-green algae, but any toxins contained in the cells will be released at once, resulting in a slug of toxins in the water. So while the bloom may no longer be visible, toxins may be present for some period of time following treatment. It is best to keep livestock away from water experiencing a bloom and wait for the bloom to dissipate on its own.
Roxanne Johnson, North Dakota State University water quality associate, says blue-green algae blooms can be accompanied by a musty, earthy, somewhat putrid odor. Concentrations of algae develop as wind moves the toxin to the shoreline, shore, where producers may find evidence of toxicity, such as dead mice, frogs and other animals near the water’s edge.
Johnson advises producers to clean stock tanks on an annual basis to keep algae growth to a minimum.
Various treatments have been used to reduce blooms, including installing aeration that reduces the competitive advantage that blue-green algae have by not allowing them to regulate their depth in the water column. Another is suspending barley straw loosely in a mesh bag in the affected pond - before algae growth begins because the anti-algae agents released by the straw are more effective in preventing algae growth than in killing algae already present. The straw becomes active within a month and will continue to inhibit algae growth up to six months.
The best way to control algae blooms is to prevent nutrients from entering the pond. Keep a 30-foot grass buffer around the pond. If that is not practical, provide as large a buffer as possible. Do not allow livestock to create mud lanes or regularly graze the buffer area. Eliminate activities around the pond that can create more nutrient loading from surface water runoff, such as bare ground areas.