I am in Providence, Rhode Island, attending the "International Didymo Conference," where scientists and policy experts from around the world have gathered to talk about this aquatic invasive species. If you're not familiar with the diatom Didymosphenia geminata, you should be. "Rock snot," as it is often called, has the ability to spread quickly. For example, since the first blooms of this alga were detected in one river on New Zealand's South Island in 2004, it has infiltrated many other major river systems there (fortunately it has not spread to the North Island). And it's a growing concern here in the United States as well.