On October 27, 1950, the Washington State Game Department uses rotenone — a natural toxin produced by a variety of plants native to South America, Australia, and Asia — to kill more than 660,000 fish in Green Lake in Seattle. The dead species include northern pikeminnow (then called squawfish), suckers, perch, stickleback, and rainbow trout. Because the rotenone does not poison the fish, they are edible when they die, and numerous people come to collect them. The state will continue to use rotenone until 1976.
During the last Ice Age, a sheet of ice known as the Puget lobe of the Cordilleran Ice Sheet pushed south out of Canada between the Cascade and Olympic Mountains to just south of Olympia. The ice was 3,000 feet thick in the Seattle area. When it retreated, or melted, back to the north, pieces of the glacier calved off and, if they melted in a depression, formed lakes. Green Lake is a small lake that formed in this manner around 16,000 years ago. Geologists call such lakes kettles. Surface runoff from the surrounding hills and small creeks continued to provide a supply of water.
Coast Salish people have lived for millenia near the lake. A mile or two east along its outlet, Ravenna Creek, was the village of sluʔluʔwiɬ, and less than a mile to the north is líq’təd (Licton Springs), a spiritually significant place (and a City of Seattle landmark). The lake would have been a good source of freshwater resources, including fish, waterfowl, and plants.
In 1910, based on the suggestions of landscape architect John Olmsted (1852-1920), the city began to alter the lake’s original shoreline, lowered it by six feet, and directed the flow of Ravenna Creek into the newly built North Trunk Sewer. Faced with a variety of water-quality issues over the years, as well as changes in recreational needs, the city has regularly adapted the park and its surroundings, including stocking the lake with rainbow trout, beginning in the 1940s. As fishing became more popular, people apparently also stocked the lake with fish they wanted, as well as requested that the lake be more suitable to valued fish such as rainbow trout. In response, State Game Department officials used 10,000 pounds of rotenone in 1950 to kill every fish in the lake. They did so by towing gunnysacks through the lake, leaving behind a "yellowish muddy wake" ("Green Lake Fish ...").
Rotenone is a naturally occurring chemical (C23H22O6) found in the roots of several tropical plants in the Pea (Legume) family, including derris (Derris elliptica from Asia), barbasco (Lonchocarpus utilis from South America), and the Florida fishpoison tree (Piscidia piscipula from North America). Long used by Indigenous people to kill (or stupefy, as one writer described the process) fish for food, rotenone began to be used in the middle 1800s as an insecticide, and is still used for that purpose. On July 17, 1934, Carl Hubbs (1894-1979), Director of Michigan’s Institute for Fisheries Research, first used rotenone to kill fish in the United States. He applied it to two small ponds to kill goldfish and carp. Several thousand fish died, though not all of them.
Targeting the Undesirables
Washington began to use rotenone in September 1940, at Kings Lake in Pend Oreille County. According to a January 2002 Environmental Impact Statement produced by Washington Department of Fish and Wildlife, in the 62 years since the state started using rotenone, employees applied it to 508 lakes and ponds, targeting numerous species including pumpkinseed sunfish, carp, crappie, and largemouth bass, all non-native fish introduced to the state by the United States Fish Commission in the 1890s. In urban settings, such as in Snohomish and King counties, targeted fish were often ones illegally introduced (meaning by individuals or groups), such as yellow perch, blue gills, channel catfish, and fathead minnow.
"Green Lake Fish Population Dies by Poisoning," according to a headline in the Seattle Post-Intelligencer the day after the state made its initial application of rotenone at Green Lake on October 27, 1950 ("Green Lake Fish ..."). More than 660,000 fish died, including three-spine stickleback (45.1 percent of the total), yellow perch (22.6%), unidentified sucker (15%), northern pikeminnow (7.5%) – a fish long known as squawfish but whose racist name was changed in the late 1990s – brown bullhead (7.5%), and largemouth bass (2.3%). (It’s hard to say exactly what fish were originally in Green Lake, but stickleback, suckers, and pikeminnow are native regionally.) State game officials typically labeled these fish as scrap fish, though Clarence Pautzke, the state’s chief fish biologist, also described them as "a horde of lusty, finny squatters, voracious usurpers ... and underwater marauders" ("Kill or Cure ...").
Newspapers also noted that hundreds of people were there to watch, and to reap the dead fish. Rotenone does not make the fish inedible because the fish suffocate and retain minimal amounts of the toxin, mostly in inedible parts. In addition, cooking breaks down the chemical, further reducing risk, so the harvest of the dead fish was viewed as a positive side benefit of death by rotenone.
State officials described what they were doing as rehabilitating the lake. Cleared and cleaned of the undesirable fish, Green Lake was ready for a fresh start with more attractive species. In fact, the state is required to manage lakes in this manner. The state is the official owner of fish with legislation that mandates the enhancement and improvement of recreational fishing in this state, as well as the eradication of "undesirable" types of fish. Four months later, the Game Department planted 165,000 rainbow trout – by far the most popular game fish of Washington anglers – followed in October 1951 by 32,000 more, and another 20,000 in February, and for seven years the angling was good.
On October 30, 1957, the state again used rotenone to kill unwanted fish, which totalled 2.2 million sculpin, yellow perch, largemouth bass, and goldfish, along with rainbow trout. Five years later, also in October, 12 Game Department boats headed out onto the lake again to tow burlap bags containing 4,000 pounds of rotenone, with the usual bounty of dead catfish, perch, rainbow trout, and goldfish, and the usual bounty of observers waiting to harvest the dead fish. In late 1967, rotenone was again used, followed in 1972 by the fifth and, what would turn out to be, final application.
The state began to phase out the use of rotenone in the early 1970s and has tried a variety of additional methods to keep the lake in good shape for anglers, such as stocking grass carp to eat non-native vegetation and tiger muskellunge to control carp, alter size limits for largemouth bass, and electrofish common carp and promote their fishery. (In 1972, the U.S. Department of Agriculture required rotenone to be regulated as a pesticide. As of 2007, the EPA requires that a multipage Standard Operating Procedures manual on how to comply with the label and use rotenone in a safe and effective manner.)
Managers have also continued to stock Green Lake with fish. Since 1995, the state has stocked the lake more than 200 times with steelhead, rainbow trout, brown trout, and channel catfish. The total number of the various stages is 1.37 million fish. Other species found in the lake include brown bullhead, common carp, largemouth bass, pumpkinseed sunfish, and rock bass. It appears that the management is doing okay, as anglers still visit the lake, now actively fishing instead of waiting for death by rotenone.