The Utah Division of Wildlife Resources (DWR) in coordination with the Washington County Water Conservancy District and the U.S. Fish and Wildlife Service is conducting a treatment project to benefit and protect native fish species in the Virgin and Santa Clara rivers. The project is scheduled for October 3–8, 2011. Alternate dates for this treatment are the week of October 10 or November 7, 2011 and will be used if storms or high water delay the planned treatment.

The project includes using rotenone to chemically treat the Virgin River and the lower Santa Clara River in order to remove two invasive fish species (Red Shiner and Fathead Minnow). The Virgin River treatment section starts at the Johnson Diversion in St. George and ends downstream at the State Line Barrier near the Arizona border. The Santa Clara River treatment section begins near the town of Santa Clara and ends at the confluence of the Virgin River. Prior to the rotenone treatment, native fish will be salvaged from the treatment sections. Salvaged fish will then be moved to adjacent sections of the river that will not be treated.

Red Shiner and Fathead Minnow have recently expanded in the Virgin River drainage. Red Shiner moved upstream during last winter's flooding and Fathead Minnow invaded the lower Santa Clara River from nearby ponds. In areas where these fish have become abundant, native fish populations have declined. Past treatments have been successful in preventing invasive fish species from spreading upstream. The present project is intended to remove Red Shiner and Fathead Minnow and thereby increase available habitat for native fish.

Rotenone, the chemical used to treat the river, is a natural product derived from the roots of South American plants. Rotenone completely decomposes without leaving any harmful residues and is specifically toxic to fish. Rotenone poses no threat to other wildlife, birds, livestock, or humans at the applied concentrations. The DWR has used rotenone as a fish toxicant on many projects and has not encountered any problems with its use concerning human safety, recreation, irrigation or livestock.

In order to avoid any downstream impacts (outside of the target area) rotenone will be neutralized. Potassium Permanganate (KMnO₄), a commonly used water purifier, will be added to the stream to remove the rotenone. Although Potassium Permanganate will turn a short portion of the river purple, it is harmless and breaks down in a very short time.This project is part of the Virgin River Program which is a collaborative effort among local, state, federal and private partners to balance human interests and conservation of the unique Virgin River system.