What is Rotenone?

Over the years, U.S. wildlife agencies have made some bad trout stocking decisions, some of which have threatened the survival of native trout species. To protect and support threatened populations, hitting the reset button on a section of water is sometimes the best option.

The idea is to remove all invasive fish, reintroduce the native fish, and let Mother Nature work from there. The most common and effective method of doing this is applying rotenone.

Rotenone is a natural compound derived from the roots of certain tropical plants. Historically used as an insecticide in gardening and agriculture, it is also an effective, efficient, and relatively inexpensive way to remove fish from a body of water.

How it Works

Once rotenone is introduced to a section of water, fish absorb it through their gills, causing them to suffocate. Rotenone doesn’t discriminate between native and non-native fish, so it must be used carefully.

What About the Native Trout?

In an ideal world, fishery managers would remove native fish from their home waters through netting or electrofishing and relocate them until the rotenone has cleared out. When that isn’t possible, sections of rivers and streams where non-native fish congregate are targeted.

A Clean Slate

Rotenone typically breaks down in a matter of weeks, and native trout can then be reintroduced to the treated section of water. What’s left is a habitat where a native trout population once thrived and may thrive again without the pressure from invasive fish.

Why Use It?

Purposefully killing trout to protect trout may seem counterintuitive, but it’s worked wonders for native populations.

Greenback cutthroats in the Poudre River watershed are a great example. Their native waters had become overrun by non-native brook and brown trout, and careful rotenone treatments removed those fish and contributed to the Greenback population’s recovery.

A Necessary Evil

You’d be hard-pressed to find a trout angler who wants large trout populations to perish. Still, stocking programs have put many of our native trout populations in danger, and rotenone is the best option to reverse some of that damage.

A trout-killing pesticide may seem like cause for concern, but dig a little deeper, and you’ll see that rotenone plays a key role in supporting the trout populations we've put in harm's way.