Historically, the most significant threat that "killed" the fish in Lake Superior was the invasion of the Sea Lamprey, a parasitic eel-like creature that arrived via human-made shipping canals in the mid-20th century. Sea lampreys attach to large fish like Lake Trout and suck their blood; a single lamprey can kill up to 40 pounds of fish in its lifetime. By the 1950s and 60s, the Lake Trout population had collapsed by 95% due to a combination of lamprey predation and commercial overfishing. In 2026, however, the story is one of recovery. Decades of aggressive "lampricide" treatments and strict fishing quotas have allowed the Lake Trout to be officially declared restored and self-sustaining in Lake Superior. While invasive species like Zebra Mussels and Round Gobies continue to disrupt the ecosystem by hogging nutrients, the "mass killing" era of the sea lamprey is largely under control. Ongoing challenges in 2026 include managing microplastics and the warming of the lake's deep waters due to climate change, which could impact the cold-water species that define the lake's fishery.