Every spring, the same anxious question ricochets through fly-fishing forums and shop talk: Is it happening yet? For fly anglers chasing bass, pike, and other warmwater species, the answer has traditionally depended on secondhand reports, gut feelings, and a willingness to drive two hours on a hunch. But there’s a better way—and the federal government has been offering it for free all along.

The United States Geological Survey’s network of more than 12,000 streamgages tracks river conditions in near real time across the country. Streamflow is the most common measurement, but many sites also record water temperature—and together, those two variables are what matter most to early-season warmwater anglers. For anglers willing to spend a few minutes learning how to read the data, these gages can replace guesswork with something close to certainty—or at least a well-informed bet. And the system works as well for Southern anglers watching February water temps as it does for Midwesterners waiting on March. Wherever the warmwater season begins earliest, USGS data may be the single best tool for catching that first productive window of the year.