As moviegoers poured into the lobby of the Lyric Theater in Harbor Springs, Michigan, last October, blood-sucking creatures—the kind that had just been featured on the big screen—were there to greet them.  

Teeming in a small aquarium, the sea lampreys elicited mixed reactions from the audience. Eel-like and squirmy, with a signature toothed tongue, their appearance was fitting for the Halloween season. Up close, it was easy to see why their nicknames include “Dracula of the Lakes” and “vampire fish.”

“Some people are just disgusted as heck with sea lampreys, though others are fascinated,” Lindsey Haskin, the writer, director, and producer of The Fish Thief: A Great Lakes Mystery, which screened that night and debuts on streaming services today, told Sierra. The film, produced in partnership with the Great Lakes Fisheries Commission and narrated by J.K. Simmons, tells the lesser-known story of this lesser-known lamprey: a fish that, if not for scientific intervention and achievement in the 20th century, would have wiped out fishing in the Great Lakes for good. “I’ve had friends tell me that lampreys remind them of the thing that comes out of somebody’s stomach in the movie Alien.”

Otherworldly thoughts were also common in the 1920s and '30s, when fishers first confronted the mysterious petromyzon marinus—a species of sea lamprey native to the Atlantic Ocean—in Lakes Ontario and Erie. They found the parasite often latched onto native fish with their jawless mouths, or simply the bloodied, circular remnants of their bites on dead schools.

Though scientists were alert to the invasive species, it remained a mystery how sea lampreys could have migrated any farther than Lake Ontario, the easternmost of the Great Lakes, which connects to the Atlantic via the St. Lawrence River. Surviving a trip through Niagara Falls, seemingly the only way to travel across the US-Canada border and westward, was considered an impossibility. But by 1938, sea lampreys had officially been identified in all five Great Lakes—a spread that baffled scientists and led to the dramatic loss of lake trout, whitefish, and perch populations.

In their native marine habitat, sea lampreys are relatively harmless parasites, leaching nutrients from much larger fish or whales. But in the Great Lakes, where native fish are physically smaller, the hosts succumb from their bites, and in great numbers. By one metric shared in the film, nearly 3 million pounds of lake trout were caught in Lake Huron and Georgian Bay in 1940; by 1946, this had dwindled to 760,000 pounds and falling.

Interviews with former commercial fishers who were forced to give up their trade bring the crisis to life in The Fish Thief. In fact, it was a race against time, Haskin says, to record the oral histories of those, now advanced in age, who lived through the bleak period. Tom Gorenflo, a fisheries biologist with the Chippewa Ottawa Resource Authority, says the same is true of many elders from the five Ottawa and Chippewa tribes he works closely with. “A lot of the old-timers have passed on,” he says.

By 1953, commercial fishing in every lake except Superior was considered dead. With fisheries devastated—and a billions-of-dollars industry uprooted—science found itself in a seemingly hopeless battle against the eponymous and pervasive thief. “It is doubtful that any attempt to curtail the increase of sea lamprey would prove practicable,” T.E.B. Pope and Carl Hubbs, two biologists whose attitudes captured the general consensus, wrote in 1938.

The Fish Thief is intentional in painting a larger picture of fishing, conservation, and society. Taking nearly seven years to complete, the film is flush with archival research. A Detroiter himself, Haskin says it was important to capture the culture and historical context of what the health of the Great Lakes means to its communities, both then and now. In many ways, the country actually has sea lampreys to thank for spurring action that led to the healthier, more equitable Great Lakes of the present day.

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“The lamprey was the proverbial straw that broke the camel’s back and jolted two jurisdictions into recognizing that if they didn’t work together to combat this existential threat, the fishery would never stand a chance moving forward,” Marc Gaden, executive secretary of the Great Lakes Fisheries Commission, told Sierra.

As recently as the mid-20th century, the United States and Canada, responsible for preserving the health of the world’s largest source of freshwater, hardly collaborated on fisheries and habitat preservation. With few exceptions, attempts to form treaties fizzled and financial cooperation stalled. If there was a silver lining of the sea lamprey invasion, Gaden says, it was the necessity to form and maintain strong binational and tribal partnerships, recognizing that economic vitality is only possible with environmental health.

The crisis was also an entryway for nontraditional fishers and recreationists to get involved in environmentalism. Even before sea lampreys arrived, overfishing and industrial pollution was rampant across the Great Lakes, placing fisheries and water quality at risk. Perhaps it should have been no surprise, then, when it was discovered that sea lampreys bypassed Niagara Falls—migrating from Ontario to Erie—through a human-made canal. As conditions worsened and fish stocks disappeared throughout the 20th century, people felt more empowered to demand change.

“The early environmental movement was very much a movement of intellectual and economic elites, the people who could afford to recreate outdoors,” says Jennifer Read, the director of University of Michigan’s Water Center. “What we saw was a democratization of the environmental movement—a demand and desire for other parts of the population to have that opportunity.”

With the health of Great Lakes fisheries hanging in the balance, scientists in the 1950s decided that a chemical solution—finding a substance toxic to lamprey and nothing else—was the best and only way forward. After years of trial and error at the Hammond Bay Biological Station in Michigan, 3-trifluoromethyl-4-nitrophenol, or TFM for short, at last proved effective in 1958. It was the 5,209th lampricide tested.

For many viewers, it may be jarring to learn that TFM lampricide is dumped regularly into the Great Lakes, still to this day. But studies have consistently shown that it has negligible effects on both other species and water quality. “Obviously, you don’t want chemicals in water; you don’t want chemicals in the Great Lakes,” Andy Buchsbaum, the vice president of One Federation and a University of Michigan lecturer, says in the film. “But chemicals are a form of pollution that dilutes. Invasive species are pollution which reproduces.”

Though sea lamprey eradication efforts were successful when TFM was introduced, with some native fish populations gradually increasing over the decades since, the story of sea lampreys in the Great Lakes will likely never have a true ending. As much as the film celebrates the restoration of the region’s fisheries, it doubles, Gaden says, as a cautionary tale.

In 2020, as a result of Covid restrictions, regional wildlife managers were temporarily prevented from spreading TFM into Great Lakes watersheds. Though this suspension was short, post-pandemic sea lamprey populations have increased in all five Great Lakes and are likely to remain elevated over the next one to two years.

“The lamprey story gives us a bit of hope that, with science and determination, we can deal with this problem,” Gaden says. “But boy, it's not a given. There are very few instances where a species like lamprey is controlled with a selective method at such a scale. Actually, I can't think of any other example.”

Keeping up a lamprey-like enthusiasm to address other threats, Gorenflo says, is essential. There are other invasive species to contend with. The introduction of invasive zebra and quagga mussels, for example, has been an ongoing problem in the region since the 1980s. When mussels filter feed, they decrease the amount of available nutrients for juvenile and larval fish. “These mussels have hit the tribes right in the crosshairs of our whitefish fisheries,” Gorenflo says.

Michigan U.P. inspecting Penguin Brand lake herring fillets in 1945.

While making the film, Haskin never wanted to denigrate lampreys—this is partly why he brought the fish to screenings around the Great Lakes region. But their homely look and destructive impact made their antagonistic characterization something natural for many to glom on to, decades ago. It’s a sentiment he hopes will soon fade. “One of the big obstacles we have to overcome is that their history in the Great Lakes has made them very villainous,” Haskin says. “They have this negative image we need to get over.”

Haskin, Gaden, and Gorenflo are similarly passionate about a story that was left on the film’s cutting-room floor: “On the Atlantic and Pacific coasts, where they're native, sea lampreys are important, valued parts of the ecosystem,” Gaden says. “And unfortunately, they're on the ropes. They’re threatened.”

In the Pacific Northwest and New England, Indigenous communities continue to harvest lampreys for food and medicinal purposes. In both oceans, sea lampreys are keystone species and natural prey for animals including salmon and eagles. As ugly as they may seem to some, sea lampreys could likely be your favorite animal’s favorite animal. “Don’t judge a book by its cover,” Gaden says. “That we're trying to get rid of them in the Great Lakes does not extend to the East and West Coasts, where we're very strongly supportive of the work that's being done to maintain the integrity of those ecosystems.”

As The Fish Thief reinforces the necessity for consistent collaboration, it is also releasing as significant leadership changes shake the Great Lakes nations. On January 6, Canadian prime minister Justin Trudeau announced he would be resigning from his office; two weeks later, Donald Trump began his second term as US president.

While upheaval brings uncertainty, especially as environmental priorities in the US appear to be rapidly shifting, there is still a thread of optimism that the Great Lakes region will sustain as a beacon of conservation priorities.

“Valuing the Great Lakes, loving the Great Lakes, and supporting restoration and rehabilitation is a bipartisan issue, and the Great Lakes Restoration Initiative receives strong Republican and Democratic support,” Read says. “My hope is that we see the Great Lakes Congressional delegation, which represents the key swing states who put this administration back in office, emphasize the importance of our region.”

Haskin hopes this message of togetherness comes across in The Fish Thief. “When you go to the Great Lakes today, you see all kinds of people. You see how fishing crosses political, social, racial, and economic lines,” he says. “The main character of the film is fishing.”