The diatom Didymosphenia geminata, also called "didymo" for short, has long been considered a cold-water, low nutrient indicator found in low abundances in northern and alpine streams and large lakes such as Lake Superior. However, in recent decades nuisance growths have appeared throughout the world including along the Lake Superior shoreline since the 2000s. In 2018, didymo was noted for the first time in a Minnesota North Shore stream that drains to Lake Superior. This webinar reports on survey work begun in 2021 that has already noted didymo in eight streams, with bloom-level abundances in four streams. Paired sampling of lake sites shows distribution of didymo in Lake Superior is limited to very nearshore depths (<2 m). We also introduce molecular approaches to determine source populations and interpopulation differences across North America.