- A new U.S. Geological Survey study compared stream and groundwater trends nationwide from 1980 to 2020.
- At many individual sites, streams grew wetter during dry spells while the water levels underneath kept dropping.
- Groundwater levels were more than twice as likely to fall as stream low flows were.
- The western United States showed drying both above and below ground, while the Upper Midwest showed wetting.
- Grouping sites by climate, land shape, and rock type gave the clearest view of how the two connect.
Friday, August 14, 2026 — A new national study has found that many American streams and the water hidden beneath the ground have been drifting apart for decades. Across much of the country, streams have often carried more water during their driest stretches over time. Yet in those same years, water levels in the ground below have kept sinking.
The study came from two scientists at the U.S. Geological Survey (USGS)
, Zachary Johnson and Michelle Walvoord. It appeared in the journal Environmental Research: Water on July 28, 2026. The agency posted a plain-language summary of the work on August 10, 2026.
A First National Look at Both Together.
Water above ground and water below ground are really one connected resource. Groundwater seeps into rivers and helps keep them running, and it supplies roughly half of the streamflow in the United States. Even so, scientists usually study streams and groundwater on separate tracks. This study set them side by side across the whole country.
The researchers pulled records from 4,992 stream gauges and 19,304 groundwater wells. They tracked changes over three time spans of different lengths: 1980 to 2020, 1990 to 2020, and 2000 to 2020. For streams, they measured “low flow,” which is the amount of water a stream carries at its lowest point in the year. For groundwater, they measured how far down a person would have to go to reach the water in shallow wells.
The Puzzle Beneath the Surface.
When the scientists looked at single sites, a strange split appeared. Streams tended to run higher at their lowest points, a sign of wetting. Groundwater levels, on the other hand, tended to drop, a sign of drying. Groundwater levels were more than twice as likely to fall as stream low flows were.
That result is puzzling because groundwater is supposed to be what keeps streams alive during dry weather. As the USGS put it in its summary, “groundwater and streamflow don’t always respond to drivers of change in the same way.” The study raises questions about how tightly the two are linked in some places.
A Country Split in Two.
The picture changed from region to region. In the West and Southwest, both streams and groundwater tended to point the same way, toward less water. In the Upper Midwest, both tended to point toward more water. The authors tied that pattern to a familiar idea, that dry areas have been getting drier and wet areas getting wetter.
Some regions showed a sharper conflict. In the High Plains and the Mississippi Alluvial Plain, stream and groundwater trends often ran in opposite directions. Those areas hold vast stretches of irrigated farmland that lean on groundwater pumping, and the study points to that heavy pumping as a likely reason the water table there keeps falling even when streams do not.
Why Streams and Wells Disagree.
The authors offered several possible reasons for the split, while noting that no single one likely explains it everywhere. In colder regions, more winter rain, mid-winter thaws, and less frozen ground can push extra water into streams in winter and early spring. Changes in the timing of low flows and in how water is managed to keep minimum flows up can also lift stream numbers. Some of that water may travel through the ground near a stream bank without ever joining the deeper groundwater system.
Groundwater also tends to move slower and steadier than streams. The unsaturated soil and rock above the water table act like a filter that smooths out short bursts of wet or dry weather. In dry regions with thick, dry ground above the water table, groundwater levels mostly track the long, slow story of recharge rather than any single storm.
Grouping Made the Picture Clearer.
The two sides of the water cycle lined up much better once the scientists grouped many sites together and looked over the longer time spans. The strongest agreement came when sites were sorted by hydrologic landscape regions, a system that blends climate, the shape of the land, and the type of rock and soil. After that grouping, only 5% to 32% of the contiguous United States showed no clear trend at all.
The Bigger Picture.
The authors wrote that the split between rising streams and falling water tables suggests a real concern. In their words, “broad-scale groundwater depletion may be ongoing even as low flow increases.” They also stressed that the country needs better and more evenly spread monitoring, especially for groundwater, and that this national overview is not a replacement for close, local study of how streams and aquifers connect.
For now, the message is that a healthy-looking stream does not always mean healthy water underground. The two can move apart, and across much of the western United States, they have.
Citation.
Johnson, Z. C., and Walvoord, M. A. (2026). As above, so below? A framework for integrating long-term water quantity trends reveals divergent patterns in groundwater and low streamflow across the United States. Environmental Research: Water, 2(3), 035008. https://doi.org/10.1088/3033-4942/ae89dd
