Rotenone treatments
A proven method used in fisheries management
Rotenone is a natural substance that comes from the roots of a tropical plant in the bean family. For thousands of years, it has been used by many cultures to kill fish, which were then harvested and eaten. Fisheries managers have been using commercially produced rotenone since the 1930s.
It's a respiratory toxin to fish and species that use gills to breathe. It is not dangerous to people, pets or other wildlife species, especially in the extremely low concentrations that biologists use to treat streams and lakes.
The goal of a rotenone treatment is to remove all the fish in a specific waterbody or part of a stream so that native fish can be reintroduced and establish healthy populations. Fisheries managers must carefully consider several factors when planning to use rotenone as a treatment method. It's used as a last resort if non-native and invasive species are overpopulating a waterbody, causing ecosystem imbalance or are outcompeting native species, like cutthroat trout. Often, other control methods — such as electroshocking and manual removal — have been unsuccessful, warranting the use of rotenone.
Rotenone use for safe, effective restoration
Wildlife agencies have safely used rotenone for decades. It is the most effective way to clear a drainage for restoration, while prioritizing public health and safety. Rotenone is used for its:
What is rotenone and how does it work?
Rotenone is a natural substance that is found in the seeds, stems and roots of tropical plants in the bean family (jewel vine and lacepod). Rotenone kills fish by disrupting the transfer of oxygen from the blood to other parts of the body such as muscles. Specifically, rotenone inhibits electron transfer during cellular respiration processes. Rotenone impacts gilled organisms like fish (and not animals that breathe using lungs) because rotenone is easily absorbed from the water into the gills.
Invertebrate and amphibian populations normally rebound quickly after a rotenone treatment is completed. In addition to being less affected overall than fish, they typically thrive when fish are absent (because fish feed on these invertebrates and amphibians). Also, the DWR does not apply rotenone to standing water adjacent to streams that do not hold fish. This means that these pockets of water will continue to hold invertebrates and amphibians that recolonize the stream.
Additionally, biologists typically schedule rotenone treatments for late summer and fall, after amphibians like frogs and toads have completed the tadpole (gill-breathing) stage of their life cycle.
The rotenone concentrations applied for our restoration projects are less than 50 parts per billion, which is well below the threshold of what is considered safe for human contact. The EPA has deemed rotenone concentrations of less than 90 parts per billion as safe for human contact, and concentrations less than 40 parts per billion are safe for drinking. And because of the rapid detoxification once rotenone is dispersed into water, actual concentrations within streams are lower than what is introduced at the point of application.
Studies have estimated that an adult would have to drink more than 10,000 gallons over a few days to receive a lethal dose at the concentrations applied by the DWR. While the product is considered quite safe in the quantities and methods used for waterbody treatment, as a precaution we close the area for public access while rotenone is active in the system and for a short time following treatment.
The American Fisheries Society (a professional society made up of fisheries biologists) has more safety information about rotenone published here.
Rotenone naturally detoxifies quickly. When water is warm, detoxification can take as little as one day. When scheduling treatments, we take into consideration that detoxification can take several weeks in colder (or deep) water. Also, rotenone readily binds to sediment and organic material in streams, which effectively removes the compound from the water. Sunlight can also accelerate the breakdown of rotenone.
Generally, rotenone will persist in the water for between one and five hours of travel time as it flows downstream. In fact, the time that it persists is low enough that when we apply rotenone, it has to be recharged at several points within the treated stream section. Simply applying rotenone at the upstream-most point and allowing it to flow downstream through the treated section is ineffective because rotenone does not persist at effective concentrations for very long.
Rotenone detoxifies quickly enough that the risk to areas downstream of the treatment site is very low. As an extra precaution, we use a counteractive product — potassium permanganate, commonly used to purify drinking water — to deactivate rotenone in situations where humans or livestock may come in contact with it. We also frequently apply potassium permanganate at the downstream end of the area treated with rotenone to prevent the unnecessary impact to fish below the treated area. Our treatments always comply with all permitting rules, which helps ensure that public safety is considered whenever rotenone is used.
Forward-looking fisheries
Careful, case-by-case management of waterbodies ensures that native species persist in Utah for future generations. This restoration work also helps keep native cutthroat trout and other species off the endangered species list.
Learn more
- Blog post: Answering your questions about cutthroat trout restoration
- Video: Living relics: Cutthroat trout restoration in Range Creek
- Video: Utah's native cutthroat trout: A journey from egg to catchable fish
- "Wild" podcast episode 57: Cutthroat restoration