Hydrologists may have a new way to study historical water conditions. By synthesizing present-day data with historical records they may be able to recreate broad hydrologic trends on a regional basis for periods from which scant data is available. Lack of reliable historical data can impede hydrologists’ understanding of the current state of waterways and their ability to make predictions about the future. That was the case for the rivers of the northeastern United States between 1600 and 1800, a period that runs from just before the first European settlers arrived to the onset of the Industrial Age.