SWWD Partners on Goldfish Management with the City of Woodbury
Goldfish are a non-native, invasive species that interrupt normal ecosystem processes when they become established in a waterbody. To protect our lakes, goldfish must be removed from stormwater ponds before they reach Powers Lake. The South Washington Watershed District and the City of Woodbury are committed to protecting our lakes.
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Goldfish (Carassius auratus) are a invasive species that disrupt lake ecosystems. They disrupt the sediment at the bottom of ponds in search of food, creating murky water. Goldfish kick up nutrients, like phosphorus, which leads to algal blooms. It is critical that these goldfish are managed before they begin to reproduce and travel. These stormwater ponds are directly connected to nearby Powers Lake. Once they enter the lake, the problem will no longer be easily solved. To protect our lakes, the goldfish must be removed from the stormwater ponds. The South Washington Watershed District and the City of Woodbury are committed to protecting our lakes.
Goldfish are a ecological problem that can be prevented. Please do not release unwanted pet goldfish, or any other non-native aquatic species into any lake, pond, or stream!
How will goldfish be removed from surface waters?
Rotenone will be used to exterminate all goldfish in the infested stormwater pond. Most of the expired fish will float to the surface and will be removed from the water for proper disposal. Some fish may sink to bottom and remain in the pond and will decompose naturally.
What is rotenone?
Rotenone is a natural compound that comes from the roots of tropical plants in the bean family. People have used it for centuries to harvest fish for food. It has been commonly used in fisheries management around the world since the 1930s.
How does rotenone work?
Rotenone works by disrupting the cellular processes that fish use to produce oxygen. It prevents them from converting oxygen into the energy needed for essential body function.
How is rotenone applied?
Generally, rotenone is added to the water from a boat. The propellers from the boat or pumps help to circulate the rotenone through the water. Backpack sprayers can also be used to apply it in smaller areas.
Is there any risk from accidentally drinking water from the pond after it has been treated with rotenone?
Regardless of rotenone, consuming water from a stormwater pond is not recommended. The public will be made aware through onsite signage. If someone unknowingly consumes treated water, the risk is very low due to the small amount used. The EPA states that rotenone concentrations below 40 parts per billion is considered safe for drinking. Chemically, rotenone is not absorbed by humans and other mammals when ingested.
Will pets or wildlife that eat fish and drink water treated with rotenone be affected?
To control fish, rotenone is applied in very low concentrations. Any residual rotenone in treated fish break down quickly. Rotenone is not easily absorbed through the digestive system. Animals who eat treated fish or drink treated water are not harmed. This means that birds, cats, dogs, and other mammals are not expected to be affected. Any rotenone ingested breaks down rapidly by the natural enzymes in the stomach.
Rotenone is absorbed directly through the gills. So animals that use gills, like fish and some aquatic insects, are impacted by the treatment. Studies show that adult frogs and most other amphibians are not significantly affected. Once rotenone breaks down, organisms are expected to recover naturally and repopulate.
Will other fish be harmed by the treatment?
Any fish in the pond will be impacted by the treatment. These stormwater ponds are directly connected to Powers Lake, a highly valuable waterbody. It is important treatment occurs before goldfish enter Powers Lake. Once they enter the lake, the problem will no longer be easily solved. There are other fish species in the stormwater pond, which have traveled from Powers Lake. After treatment, it is reasonable to expect those same fish species to return.
Why is rotenone the best tool for correcting this fishery management problems?
Previous attempts to manage the population have not been successful. Using rotenone is the only management tool that has been proven to remove all of the fish from a waterbody.
What happens to rotenone after it is applied to the water?
Rotenone is a compound that breaks down quickly in the environment. It breaks down through natural physical processes and by biological activity. The conditions that rotenone are applied under impacts its effectiveness. Warmer temperatures and increased sunlight increase the rate of breakdown.
How long does rotenone persist in water and sediment?
Studies show that rotenone residues typically break down quickly after application. Breakdown generally occurs within a few hours, depending on the conditions.
The city will treat the ponds during warmer water conditions. This will improve its effectiveness, and promote faster compound breakdown in the environment.
How long will the proposed rotenone treatment take?
Rotenone treatments and removal of the fish normally take only one day to complete.
How will the public and landowners be notified?
The city will mail letters to landowners adjacent to the pond before treatment. There will be onsite signage to notify the public of the treatment.
What are the dangers of contaminating ground water?
It is possible for rotenone to move through the soil, but it is low. Rotenone binds strongly to organic matter, making it unlikely to reach groundwater. Testing of groundwater near treatment areas show there is no detected contamination associated.
Kyle Axtell
Staff Contact
Questions? Reach out to Kyle Axtell, Planning & Projects Program Manager, at Kyle.Axtell@swwdmn.gov or call 651.728.6124.