If you grew up on any one of the Great Lakes, like I did, you may have heard of the sea lamprey—a vampiric creature that literally sucks the life out of a lake trout. As a kid, I thought they were a myth, a horror story that parents liked to tell kids on fishing trips. I wasn’t aware of the havoc this parasitic fish wrought on the entire region when it first wiggled its way from the Atlantic Ocean into the largest freshwater ecosystem on earth.

　　A new documentary, The Fish Thief: A Great Lakes Mystery, unpacks the ecological crisis created by the lamprey, sometimes called the “vampire fish,” and the extraordinary effort to contain it. “The sea lamprey is what put invasive species on the map in the Great Lakes,” says director Lindsey Haskin. “For many people, it was the first time they become aware of the scale of damage that’s possible.”

　　The Great Lakes—Ontario, Erie, Huron, Michigan, and Superior—straddle the border between Canada and the U.S. Five million people fish them every year, reeling in tasty catches like yellow perch and walleye, and even coho salmon, which was introduced for sport fishing in the late 1960s. Recreational and commercial fishing in the Great Lakes region is a $7 billion industry. Growing up in Cleveland, Ohio, on the shore of Lake Erie, my earliest outdoor memory is fishing with my dad from the Neff Road breakwall.

　　Oscar-winning actor J.K. Simmons narrates The Fish Thief. Simmons describes how sea lampreys worked their way into the Great Lakes from the Atlantic Ocean via the St. Lawrence Seaway to Lake Ontario. For most of history, Niagara Falls prevented them from spreading any further.

　　That changed in the early 1900s, with improvements to the Welland Canal, which bypasses Niagara Falls to create a shipping channel between Lake Ontario and Lake Erie. The first sea lamprey was found in Lake Erie in 1921. By 1938, sea lampreys had infiltrated the rest of the lakes, all the way to the farthest corners of Lake Superior.

　　Sea lampreys resemble eels with their long tubular shape. But their mouths are unmistakable: a suction cup lined with concentric circles of fangs, spiraling down to a toothed tongue. They latch onto other fish, create a wound with their razor-sharp teeth and tongue, and suck out blood and other fluids.

　　In the Atlantic Ocean, where sea lampreys have lived for more than 340 million years, they are mere parasites, attaching themselves most often to sharks and other sea mammals. But in the Great Lakes, very few fish are large enough to escape unscathed from a sea lamprey encounter. By the 1940s, the blood-suckers were killing their hosts—lake trout, lake whitefish, and ciscoes—in droves.

　　The region’s fishing industry began to collapse in the 1950s, paralyzing towns and Indigenous communities on every shoreline. By 1960, the annual Great Lakes catch, once around 15 million pounds of fish, had plummeted by 98 percent to a mere 300,000 pounds.

　　The Fish Thief, which has won awards on the environmental film festival circuit in North America and Europe, is the first to tell the story of the lamprey in its entirety, from the initial mystery of droves of dead fish, to the resulting ecological crisis, to the efforts to find a solution. It was eight years in the making.

　　Haskin, who grew up in the region, near Detroit, says they filmed in a variety of regions, “from the far east extremes of Lake Ontario all the way to Duluth, Minnesota, and down to Chicago.”

　　What stood out most for Haskin about the project was the tenacity of the people involved devising a solution to the lakes’ ecological collapse. “The original title for the film was Relentless, which applied to the sea lamprey, but also to the people that did battle with it,” Haskin says. “Their original ideas failed, but they just stuck to it and kept going and kept going and kept going and eventually found a solution that has been workable for almost 70 years now.”

　　Part of the challenge was the cross-border cooperation required to study, test, and, eventually, implement processes to bring the ecosystem back into balance. It required federal government oversight, which most of the fishing industry, and many of the states and provinces bordering the Great Lakes, were hesitant at first to enlist. But eventually, they ran out of options. There was nothing left to do but trust that the government (and science) could find a solution. In 1955, the U.S. and Canada formed the Great Lakes Fishery Commission, the first joint agency of its kind.

　　The commission confirmed that it was impossible to eradicate sea lampreys from the Great Lakes. But scientists could greatly reduce the invasive species’ numbers by attacking them during their larval stage, when they live as filter-feeders in lake tributaries. Some 6,000 compounds were tested to find the best “lampricide,” a pesticide capable of destroying lamprey larvae without significantly impacting other organisms, or causing long-term damage to the ecosystem.

　　Administering the pesticide to larvae in tributaries, as well as using barriers and traps to prohibit full-grown sea lampreys from making it out of the tributaries into the Great Lakes, cut the “vampire fish” population by 90 percent. The Great Lakes Fishery Commission, in partnership with U.S. Fish and Wildlife Service, Fisheries and Oceans Canada, and the U.S. Army Corps of Engineers, has been working to keep sea lampreys at that benign level ever since.

　　The sea monster of my youth is real. The next time someone from back home brings up sea lampreys, I’m going to have a whole lot more to add to the story.

　　The Fish Thief: A Great Lakes Mystery is set to release on January 31, 2025 in the U.S. and Canada, where it will be available to stream, download, or rent on platforms including Apple TV/iTunes, Amazon, Google/YouTube, and Tubi.