Pine Bluff, Arkansas – Blue-green algae, also called cyanobacteria, are found every summer in Arkansas, said Scott Jones, a small reservoir augmentation specialist at the University of Arkansas at Pine Bluff. The hottest season is typically when potentially harmful blue-green algae blooms are most common, due in part to temperature, but mostly to the buildup of nutrients.
In summer, rainfall is less frequent and water loss through evaporation concentrates nutrients. The worst blooms occur in ponds with heavy organic buildup (silt), excessive fertilization or fish feeding, or when the land draining into the pond is over-fertilized or produces excessive organic waste (especially near heavy poultry production because the waste contains a lot of phosphorus) and in ponds where livestock have uncontrolled access to the water, Jones said.
“When the algal blooms are dense enough to cause health problems, they usually take the form of floating surface foam that looks like spilled paint and comes in shades of light green, blue, red, gray and several shades in between,” he said. “A quick way to identify blue-green algae is to dip a stick into the surface foam. If the stick comes out covered in foam, like paint, it is likely blue-green algae foam.”
Placing a water sample with some foam in a glass jar that sits in the refrigerator overnight can also provide evidence. If a ring of the foam is still floating on the water’s surface in the jar the next morning, it’s probably blue-green algal foam, Jones said. Other floating plants such as watermeal, azolla, duckweed and even some floating segments of underwater plants can sometimes be misidentified as algal foam.
“Blue-green algae are photosynthetic bacteria that can crowd out beneficial green algae. Of the few thousand species of blue-green algae, some can produce neurotoxins or liver toxins that can cause illness or even death in animals hours to days after ingestion,” he said. “Fish are also susceptible to these toxins, and significant mortality can occur in excessive blue-green algae blooms.”
Potentially toxic blue-green algae do not always produce toxin. The only way to confirm the presence of toxin is through laboratory testing, he said.
In addition to several private labs, the Arkansas Water Resources Center Water Quality Lab can identify algae and test for the presence of algal toxins, Jones said. Contact the lab at (479) 502-9843. For a list of other appropriate labs, contact the Arkansas Department of Environmental Quality at (501) 682-0744. Analysis can take several days, so avoid exposure and keep animals away from affected water until results are available
Blue-green algae blooms can be treated with aquatic herbicides containing copper sulfate or sodium carbonate peroxyhydrate. Animals should be kept out of the pond for at least a week after herbicide treatment because toxin levels will likely temporarily increase as the herbicide kills the blue-green algae, Jones explained.
“Herbicides in most cases only provide two to three weeks of relief before the algal bloom returns. Long-term control requires a nutrient binder that removes phosphorus from the water, slowing the return of the algal bloom,” he said. “Use a commercial flocculant (brand examples include EutroSORB G, Phoslock or Phosclear) about a week after the herbicide application. It may take a few cycles of this treatment (herbicide/flocculant) throughout the year to slowly bring nutrients and algal blooms back under control.”
Water dyes, particularly those containing Acid Yellow 23, which are registered with the EPA, may help somewhat in suppressing algal blooms, Jones said. There are no practical biological control agents. The best solution is prevention by minimizing nutrient input from fertilizer runoff, poultry manure, animals loitering/wading in the pond and overfeeding fish.
“Old, shallow livestock ponds (less than 3 feet average depth) may be better served with a complete renovation; draining and excavating accumulated sediment, restoring bank slopes, and deepening the pond back to at least 4 feet average depth and up to 10-12 feet maximum depth,” he said. “If renovation is considered the best solution, strongly consider installing external irrigation systems and fencing the pond from animal contact.”
For more information about blue-green algae in ponds, contact Jones at (870) 575-8185 or (email protected) or your local county office.
