Harmful Algal Bloom Toxins – and How They Affect Animals



 before and after of algaecide treatment of harmful algae bloom  

Causes of Harmful Algal Blooms

A common theory is that humans have added nutrients to the water that produce harmful algal blooms. However, the causes are not that simple and there is no evidence in literature to prove that reducing fertilizer use or removing septic tanks have ever reduced the likelihood of the proliferation of an algal bloom.

Surface waters reflect watershed condition but they are also subject to the considerable influence of the bottom sediment, where nutrients hide. Invasive plant and animal species, which include algae and microbes, are constantly being introduced to surface water and they also have a dramatic impact on the condition of surface water resources. 

Generally, algae proliferate in warm temperatures and stagnant water but nuisance conditions are not limited by temperature and water flow. They’re opportunistic organisms, and extreme weather events like record high temperatures, drought, or flooding or man-made changes to the environment may exacerbate their growth.

Increasingly, pets, livestock, wildlife, and crops are more at risk from exposure to algal blooms, but this can be avoided.

Dr. John H. Rodgers, Director of the Ecotoxicology Program at Clemson University, and a pioneer in the study of harmful algal blooms says, “Having a plan to address algal blooms is the best way to protect pets, livestock, fish, wildlife, and humans. The “do nothing” solution is not an option and avoiding the water is a poor option.” 


Cyanobacteria and Health Effects

Many harmful algal blooms are produced by cyanobacteria (aka “blue-green algae”), a photosynthetic bacteria that can produce toxins.

Cyanobacteria can produce liver toxins, neurotoxins, and endotoxins. Fresh water diatoms, golden algae and some brown algae also produce toxins. Symptoms in humans and animals include muscle cramps, nausea and vomiting, diarrhea, paralysis, cardiac or respiratory difficulty, and liver failure. Death for fish, wildlife or animals can occur within hours or days.

Threats to Pets and Livestock

Drinking from ponds showing signs of a harmful algal bloom may prove fatal to pets, horses and livestock. Dr. Rodgers investigated an Angus cattle kill in North Georgia.  Dr. Rodgers reports that the cattle were drinking from a farm pond and died from microcystins that were in the water.

Unfortunately, cattle and dogs willingly drink water affected by harmful algal blooms and even eat algae mats. Dogs are also put at risk when exposed to cyanobacteria after licking their fur after swimming in the water.

Toxic Algae Threats Across the Country

Cyanobacteria toxins killed 32 head of cattle in Lake County, Oregon in June 2017. In Napa, California,two dogs died after swimming in a pond with a blue-green algae bloom. In 2018, seven dogs became ill from toxic algae in Lake Okeechobee in Florida. In 2011, dogs were harmed from an algal bloom in Kansas.


Threats to Fish and Wildlife

Fish can also be susceptible to harmful algal blooms, especially in aquaculture. Dr. Rodgers noted an aquaculture farmer in Mississippi who lost one million fish in a day due to a harmful algal bloom. The associated cost for the farmer was $1 million.

Cyanotoxins can even affect marine mammals. Dr. Melissa Miller of California’s Department of Fish and Game was lead author of a paper documenting the death of 21 southern sea otters. Dr. Miller reported that the otters died of microcystin poisoning after eating shellfish with concentrated levels of the toxin. A freshwater lake a mile inland was affected by a blue-green algal bloom, and tributaries carried cyanobacteria to Monterey Bay.

Dr. Susan Wilde, University of Georgia, conducts research onavian vacuolar myolinopathy (AVM). AVM is a deadly brain disease affecting baldeagles and American coots. Cyanobacteria grow densely on invasive aquaticplants which are eaten by ducks, geese, and coots. Sick or dead waterbirds areeaten by bald eagles, which then die from the toxin as well. Arizona’s Tempe Town Lake experienced a fish kill inthe thousands after an outbreak of golden algae. Southwest Florida was massively impacted by a bloomthat affected marine life - like those protected by the Endangered Species Act,the Florida manatee.


What to Do in Case of Exposure

For humans and domestic animals, get away from the water quickly. Get medical help as soon as possible.

Preventing Exposure to Algal Toxins

With early intervention and actively managing the situation, a potential algal bloom can be prevented altogether. Dr. Rodgers notes that “Dead algae don’t produce toxins.”

Act Quickly - When a problem appears, early detection and rapid response are critical and water resource managers, including farmers and city officials, must be observant.

A successful short-term response uses algaecides to kill the algae. Copper-based formulations such as Cutrine ® Ultra or Algimycin® Algaecides have been proven to kill algae and cyanobacteria by interfering with enzyme production. Non-copper formulations like Phycomycin® Algaecide are oxidizers, and quickly get to work, destroying the cell walls. A great way to determine which product to use is The Algal Challenge Test, which looks at the most effective algaecide to control algal concentration, while using the least amount, a prescriptive water management approach.

Aquashade® Prevent Harmful Algae Blooms with a Registered Dye

Aquashade® Aquatic Plant Growth Control is EPA registered to control cyanobacteria. 

cutrine ultraAn Algal Challenge Test done on Pawnee Reservoir in Nebraskasuccessfully predicted a treatment of Cutrine® Ultra Algaecide ontoxin-producing algae. 

Keep monitoring and treat early – Waters that are prone to harmful algal blooms require proactive management that includes post-treatment monitoring and follow-up treatments. A diligent lake and pond management program will help reduce the risk of future harmful algal blooms affecting pets and livestock.