Goldfish are a non-native, invasive species that interrupt normal ecosystem processes when they become established in a waterbody. They actively disturb pond bottom sediments in search of food, causing low water clarity. This also makes nutrients like phosphorus available for algae to use, leading to unwanted blooms. It is very important that goldfish are not allowed to establish reproducing populations in our lakes. Removing them from stormwater ponds before they reach our lakes is a critical activity that the City of Woodbury and South Washington Watershed District are committed to.
Please do not release unwanted pet goldfish, or any other non-native aquatic species, into any lakes, ponds or streams!
How will goldfish be removed from surface waters?
Rotenone will be used to effectively and efficiently exterminate all goldfish in an infested pond. Most of the expired fish will float to the surface where they will be harvested and removed from the water for proper disposal. Some fish may sink to bottom and remain in the pond where they will naturally decompose.
What is rotenone?
Rotenone is a naturally occurring compound derived from the roots of tropical plants in the bean family. People have used it for centuries to harvest fish for food. As a piscicide—a substance that is toxic to fish—it has been widely used in fisheries management around the world since the 1930s.
How does rotenone work?
Rotenone disrupts a key cellular process, preventing fish from using oxygen to produce the energy needed for essential bodily functions.
How is rotenone applied?
Rotenone can be applied in either a wettable powder or liquid form. Depending on waterbody characteristics, rotenone is typically pumped into the water from a boat. The propeller wash from an outboard motor or pumps can help circulate the rotenone through the water. Backpack sprayers can also be used to apply rotenone to smaller areas.
Is there any risk from accidentally drinking water from the pond after it has been treated with rotenone?
Drinking water from any stormwater pond is not recommended whether or not it has been treated with rotenone, and the public will be informed through onsite signage. However, even if someone unknowingly consumed treated water, the risk would be very low due to the small amounts used. The EPA indicates that rotenone concentrations below 40 parts per billion are considered safe for drinking, and most treatments result in levels well under this threshold. In addition, rotenone is not readily absorbed by mammals when ingested.
Will pets or wildlife that eat fish and drink water treated with rotenone be affected?
To control fish, rotenone is applied at very low concentrations. Residues in treated fish are minimal, break down quickly, and are not easily absorbed through the digestive system of animals that may consume them. As a result, birds, cats, dogs, and other mammals are not expected to be affected by eating treated fish or drinking treated water. Any rotenone ingested is rapidly broken down by natural enzymes in the stomach and intestines.
Animals that rely on gills, such as fish and some aquatic insects, are more sensitive because rotenone is absorbed directly through the gills. In contrast, studies indicate that adult frogs and most other amphibians are not significantly affected. Any short-term reductions in sensitive aquatic insects or similar organisms are expected to recover naturally once rotenone breaks down and the area is recolonized from nearby habitats.
Will other fish be harmed by the treatment?
Because rotenone affects all gilled organisms, any fish currently in the pond will be impacted. During initial goldfish removal efforts in 2025, a fish survey identified two additional species besides goldfish: fathead minnows and brook sticklebacks. These species are commonly found in stormwater ponds and are expected to repopulate naturally after treatment, as the pond is connected to other nearby stormwater systems where these fish are likely present.
Why is rotenone the best tool for correcting this fishery management problems?
Using rotenone is the only management tool that has been proven to remove all of the fish from a waterbody. Previous electro-shocking efforts have not been successful in removing goldfish from stormwater ponds.
What happens to rotenone after it is applied to the water?
Rotenone is a compound that breaks down quickly in the environment. It is degraded through natural physical processes and by biological activity. Warmer temperatures and increased sunlight further speed up the rate at which rotenone breaks down.
How long does rotenone persist in water and sediment?
Monitoring studies indicate that rotenone residues typically break down quickly after application, generally within a few hours, depending on environmental conditions. Breakdown occurs more rapidly in warmer temperatures and with increased sunlight.
The City has planned the Rotenone treatment to be applied during warmer water conditions to improve its effectiveness on fish while also promoting faster natural degradation in the environment.
How long will the proposed rotenone treatment take?
Rotenone treatments and removal of the fish within the City will normally take only one day to complete.
How will the public and landowners be notified?
The City will mail notifications to landowners that live in neighborhoods directly adjacent to a treated surface water prior to any application. There will be onsite signage notifying the public of the treatment.
What are the dangers of contaminating ground water?
Rotenone has a low potential to move through soil. It binds strongly to organic matter, making it unlikely to reach groundwater. Monitoring studies of groundwater near treatment areas have not detected contamination associated with rotenone use.
Questions?
Contact Kyle Axtell, Planning & Projects Program Manager, at [email protected] or at 651.728.6124.