Several years ago, while doing research in the Great Western Sugar archives—currently housed at Colorado State University—I stumbled across a 1918 report authored by Max Ellis, a fisheries biologist at the University of Colorado. It is likely that Great Western commissioned the study. Upon viewing its findings, company executives labeled it ‘confidential,’ and filed it away. Inside the report, Ellis recorded the macabre details of massive fish kills in the reservoirs and streams where the sugar company dumped its wastes. The study was stunning in its description of how company wastes suffocated fish by sucking the oxygen out of the water.[1]

As an expert on the fish species of Colorado, Ellis was able to record the names of each species floating lifelessly on the water. Even in 1918, most of these fish were not native to the region.[2]

In 2024, I visited some of the waters where Ellis conducted his field work. Fossil Creek Reservoir in Fort Collins is one such place. As I wandered one of the pleasant trails that meander above its shoreline, I heard loud splashing at uneven intervals. So, I beat a path down to the water’s edge. As the trees and brush cleared on my approach, I observed fish, aggressively targeting surface insects. The fish were caramel-colored, thick-bodied and marked by scales that were exposed each time they arched their backs into the water after feeding. I immediately recognized them as carp. During the hour I spent on the banks of Fossil Creek, I did not see another fish species.

Common Carp are just one example of more than twenty invasive fish species that dominate reservoirs such as Fossil Creek and throughout the region. How did they get there? In the archives at Colorado State University and within the libraries and museums in the Fort Collins area, I found my answer.  

When Anglo settlers began arriving in Northern Colorado after the Civil War, most of them had water on their minds. Seeking to transform the dry Northern Colorado Plains into a collection of farming enterprises, they diverted most of the South Platte River watershed’s paltry 1.6 million annual acre-feet of water. Within a decade, they codified what historians refer to as the Colorado Doctrine, which enabled users to claim a specified quantity of water based on how much they could put to ‘beneficial use,’ prioritizing access on the order of their claims (‘first in time, first in right’). With all of the watershed’s natural flow tapped by the 1880s, water users pooled resources to build dams and other infrastructure, dotting the region with more than one-hundred impoundments by the early twentieth century.[3]

Seeking to further monetize their water holdings, many of the region’s farmers built fish ponds in the 1880s. They were influenced by the growth of private hatcheries in Colorado that advertised the sale of invasive warm water species. Initially, this meant carp. Regional and national publications such as Field and Farm, Colorado Farmer, and The American Angler boasted that various species of the fish—especially German Carp—grew rapidly on farm surpluses and were in demand in the nearby Denver market. They instructed farmers on “How to Make a Carp Pond,” and argued that a well-managed thirty-acre pond could yield “twenty tons for the market,” since carp grow at a rate of up to five pounds each year on minimal expense. Many farmers took the bait.[4]

Nature quickly revealed that ponds were not sealed aquatic systems. During periods of high water and floods, pond banks overflowed, flushing carp into irrigation ditches. Some of those ditches were connected to larger canals, while still others drew water directly from streams such as Fossil Creek and its namesake reservoir. Hoping to cash in on carp, some irrigation companies and reservoir operators planted carp directly into these bodies of water. And, since just about every human-built water conveyance in Northern Colorado was connected by a system of ditches, canals, and reservoirs by the early twentieth century, it did not take long for carp to migrate throughout the system.[5]

Unsurprisingly, hatchery operators, farmers, and publishers had oversold a species with limited appeal. By 1890, fish mongers and consumers in the Denver market were revolting. The same publications that formerly praised carp now concluded that the fish were “not fit for human consumption because of its rank smell and taste,” and that consumers had “boycotted carp on account of its rank individuality.”[6]

Over the next two decades, they encouraged enterprising irrigators and reservoir operators to stock their ponds with a whole set of invasive species that included catfish, bass, sunfish, and perch, supplied by private hatcheries in several plains states. As these new species found their way into farmers’ ponds, storms washed many of them back into ditches. The same infrastructure that moved water onto farms could redirect fish away from them.

In the meantime, as irrigation companies and private operators built reservoirs, they stocked them with desirable species, often with the goal of eradicating carp. Burton Sanborn was one such operator. Sanborn created the North Poudre Irrigation Company in 1901 out of existing irrigation companies. It supplied water to thousands of acres of Northern Colorado farmland. Seeking to bolster water supplies, Sanborn built Fossil Creek Reservoir in 1902 and nearby Boyd Lake in 1904. Immediately, carp invaded.[7]

This presented problems for Sanborn since he also hoped to draw anglers to his lakes. So, from 1907-1909, he researched species that could outcompete carp and attract anglers. Some suggested Pickerel (Walleye), but Sanborn learned that this fish was aggressive enough to kill off other desired species. So, after extensive correspondence with officials at the U.S. Bureau of Fisheries, he settled on Black Bass, which they argued would outcompete carp. For good measure, Sanborn also ordered thousands of non-native catfish. The bass and catfish arrived by train. So, whether by ditch or rail, Sanborn’s reservoirs contained populations of multiple invasive species.[8]

While no fish surveys exist of either reservoir, we do have some ideas about how they fared..., from the work of Max Ellis. As farmers, irrigation companies, and reservoir operators reconfigured the region’s infrastructure and aquatic life, Ellis studied the consequences, quietly becoming the region’s foremost expert on its fish. This would attract the attention of Great Western Sugar, Northern Colorado’s most important economic driver, and its most significant polluter.

More on that in my next post.

[1] Max Ellis, “Report of the Investigations Concerning the Pollution of Streams and Reservoirs by the Various Sewages from the Factories of the Great Western Sugar Company,” February 25 1918, Records of the Great Western Sugar Company, Agricultural and Natural Resources Archive, Colorado State University.

[2] Max Ellis, Fishes of Colorado (Boulder: University of Colorado Press, 1914).

[3] On the origins of the Doctrine of Prior Appropriation see David Schorr, The Colorado Doctrine: Water Rights, Corporations, and Distributive Justice on the American Frontier, Yale Law Library Series in Legal History and Reference (New Haven CT: Yale University Press, 2012); On Northern Colorado's early use of irrigation water see Robert G. Hemphill and United States, eds., Irrigation in Northern Colorado, Agric. Dept. Bull. No. 1026 (Washington: U.S. GPO, 1922); Rose Laflin, Irrigation, Settlement, and Change on the Cache La Poudre River (Colorado Water Resources Research Institute, Colorado State University, 2005); Elwood Mead, Irrigation Institutions; a Discussion of the Economic and Legal Questions Created by the Growth of Irrigated Agriculture in the West, Use and Abuse of America’s Natural Resources (New York: Arno Press, 1972).

[4] I examined a selection of articles in The American Angler, The Colorado Farmer, and Field and Farm from 1884-1894. Field and Farm published a regular column called “The Fish Pond,” beginning in 1888, that was particularly useful. See Field and Farm, (Denver: Field and Farm Pub. Co.); The American Angler, (New York: The Angler’s Publication Company); The Colorado Farmer (Evans, Colo: J.C. Febles and L.A. Phillips).

[5] One example of this can be found in “How to Make a Carp Pond,” Field and Farm, April 17, 1886.

[6] See for example “The Fish Pond,” Field and Farm March 22, 1990.

[7] For a brief history of the North Poudre Irrigation Company see Orsi, Jared, “North Poudre Irrigation Company, 1901-Present,” (Fort Collins: Public and Environmental History Center), available from https://pehc.colostate.edu/digital_projects/dp/poudre-river/moving-storing/let-the-water-flow-ditch-companys/north-poudre-irrigation-company/.

[8] Between 1907 and 1909, Burton Sanborn communicated extensively about locating and purchasing fish that would reduce carp populations and attract anglers. See for examples George M. Bosers, U.S. Fisheries Commissioner, to Burton Sanborn, September 30 1907 and November 10 1908, Burton D. Sanborn Collection, Hazel E. Johnson Research Center, City of Greeley Museums, Box 1.