Smallmouth bass are native to much of the midwestern USA and central Canada, but have been introduced to 41 states and 20 countries. While they are sought-after angling targets, they also are voracious predators of small fish and crayfish, which is of particular concern given their taste for baby salmon and trout. Thus it is crucially important for management and conservation to detect which streams have been occupied by smallmouth bass. Current methods involve snorkeling through streams, but this is expensive, time-consuming, and not guaranteed to detect all occurrences. In a new study, the methods of environmental DNA (eDNA) is trialed that involves taking a water sample and testing it for cast-off bits of DNA from smallmouth bass. The eDNA tests detected smallmouth bass in streams at similar or greater rates than snorkel surveys, and was able to distinguish between smallmouth and largemouth bass DNA, but could not distinguish between smallmouth bass and a couple of other closely related species occurring outside the Pacific Northwest. Thus the new method is perfectly suited for surveying streams in the Pacific Northwest for smallmouth bass, with much less environmental impact than snorkel surveys. The study was conducted by Thomas Franklin and colleagues at the U.S. Department of Agriculture, together with SAFS PhD student Erika Rubenson and SAFS professor Julian Olden, and appears in the journal Northwest Science.