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green algal bloom

Managing Algal Toxins in Pond Water

algal growth in a pasture pond

algal growth in a pasture pond

As temperature goes up, is your pond water facing the algal blooms? Do you know about algal toxins?  Blue-green algae (cyanobacteria) are common algae that generally float in the water column or attach to the pond bottom or a rock, piece of wood or other surface in the pond. Toxic algae is the name given to a few species of algae that produce chemicals that irritate skin, damage the liver or affect the brain. These effects can be quite serious, but generally are not.

Why do common algae suddenly produce toxic chemicals?

Dry weather is mostly responsible for the development of toxic algae conditions. During a drought, pond water volume is reduced and runoff no longer flushes the pond. Reduced water volume concentrates phosphorus and other nutrients that are dissolved in the water. Phosphorus, nitrogen, heat and sunlight allow algae to grow at a rapid rate. Certain blue-green algal species can dominate the algal population to the point of becoming a single species bloom. Toxins form inside the blue-green algae cells and may be released into the water directly or after the cells die and are disrupted. Pond water with a small amount of toxin may suddenly have a large amount after blue-green algae is killed with an algicide or by a change in light or nutrient amounts. These events are called “sudden death,” “dieoffs,” “turnovers” or “death phase.”

What can be done to prevent animal deaths?

  • Watch for the development of algal blooms in ponds.
  • Watch animal behavior.
  • Use algae control methods to minimize the chance that dense algal blooms that favor toxin production will develop.
  • Control nutrients that reach the pond water to limit algal growth.
  • Maintain grass buffers around the pond edge to catch or filter nutrients from animal waste or crop fertilization.
  • Allow animals to water in limited areas of the pond or pipe pond water to tanks located away from the pond edge to limit manure contamination from animal access.
  •  If algal blooms do develop, take steps to eliminate the danger of algal toxins.
  • Watch ponds with stagnant water carefully.
  • Consider algal control methods when algal blooms limit visibility to less than 12 inches into the water.

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