The Great Lakes Fishery Commission and the Great Lakes Commission have launched a mapping application that offers the ability to trace the effects of dams and dam removal on sea lamprey populations in the Great Lakes. Sea lampreys, which are invasive in the Great Lakes and destroy fish with a voracious appetite, need certain stream types for spawning. Unfortunately, the Great Lakes basin is abundant with sea lamprey streams. Dams and barriers, which inhibit fish passage, serve a sea lamprey control function and protect millions of Great Lakes fish from sea lamprey predation. This online tool helps researchers, policy-makers, and the public visualize Great Lakes barriers and dams and better understand the benefits and drawbacks of dam removal.