Chattahoochee River National Recreation Area

This guide to the Chattahoochee River National Recreation Area in Atlanta follows a hydrologist wading into the river with a sample bottle, chasing a bacteria count that used to take two days to come back from a lab. It traces how the United States Geological Survey, the National Park Service and the nonprofit Chattahoochee Riverkeeper set out to close that gap, and how the resulting system, called BacteriAlert, has quietly run for more than two decades under Island Ford. Three of its sensors sit inside this recreation area right now, reading the river as you walk beside it.