Understanding Copper Sulfate’s Effect on Ponds

Understanding Copper Sulfate's Effect on Ponds
Copper Sulfate

Understanding Copper Sulfate’s Effect on Ponds

Copper sulfate is an inorganic compound that is used as a biocide to kill bacteria, algae, roots, plants, snails, and fungi. Copper sulfate is highly toxic to fish. Even at recommended rates of application, this material may be poisonous to trout and other fish, especially in soft or acid waters. The toxicity of copper sulfate depends on the copper content. As an element, copper can persist indefinitely. Copper sulfate has been registered for use in pesticide products in the United States since 1956.


Utilize subsurface aeration. Regardless of the copper product used, there is always a risk of oxygen depletion following herbicide or algaecide applications. The bacterial decomposition of organic matter requires a substantial amount of oxygen. High biomass kills (dying algae) may result in decreased oxygen levels that lead to fish mortality.


Sensitivity to PH. Water sampling and testing should be performed before applying a copper sulfate. Aquatic labeled herbicides containing copper state the products should not be used if alkalinity and hardness levels are below 50 ppm. Applying copper products in soft waters will increase the amount and time that the copper is available in the water, thus increasing exposure of fish to copper.

Oxygen Depletion. Under conditions of heavy infestations, treat only 1/3 to 1/2 of the water body at a time. This avoids fish suffocation caused by oxygen depletion from decaying algae.

Growing resistance. Blue-green algae in some copper sulfate-treated Minnesota lakes became increasingly resistant to the algaecide after 26 years of use.

Indefinite Persistence. Copper is bound, or absorbed, to organic materials as well as clay and mineral surfaces. The degree of absorption to soils depends on the acidity or alkalinity of the soil. Because copper sulfate is highly water soluble, it is considered one of the more mobile metals in soils. However, because of its binding capacity, its leaching potential is low in all but sandy soils.

Ecosystem instability. Overuse of copper sulfate can lead to systemic weakening of the pond and lake ecosystem, making the water body uninhabitable to native species and more attractive to undesirable species.

This edition of PondHawk BRIEFS is curated from the following sources:

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