Can Human-Built Beaver Dams Make Up for Lost Snow? A USGS Test in New Mexico

The Rio de las Vacas, New Mexico, December 2025. Photograph by Justin Nichols, U.S. Geological Survey

In northern New Mexico, rivers and streams have long been fed by mountain snow. That supply is failing, and many streams now run dry or nearly dry in summer. The U.S. Geological Survey (USGS) is testing a low-tech fix borrowed from nature: beaver dam analogs (BDAs) — human-built structures across a stream that mimic what beaver dams do.

Less snow, earlier melt

In the Jemez Mountains:

Figure 1: the shift from snow to rain (A) and the earlier melt-out date (B) in the Jemez Mountains. Image from the USGS fact sheet

Climate models project that over the next 50 years New Mexico will grow drier, warm by 5–7 °F, and see more winter rain instead of snow. The snowpack that once carried streams through summer is becoming unreliable.

Why base flow matters

Base flow — the groundwater that seeps into a stream — keeps water flowing through summer and drought, and gives aquatic life refuge in extreme heat and cold. It's closely tied to snowpack and how long snow lies on the ground: bigger snowpacks let more water soak in and recharge the ground.

Base flow in northern New Mexico streams declined from 1980 to 2015, and in the Colorado River Basin, to the west, it could fall another 33% by century's end, most steeply in mountain headwaters.

Rain runs off far faster than melting snow, so less soaks in. What's needed is a way to "slow the flow."

What beavers do

Beavers are ecosystem engineers: their small dams create ponds. Dams:

• slow streams and store surface water
• lower flood peaks from intense storms, such as monsoon downpours
• raise the groundwater table nearby by increasing infiltration
• reconnect streams to floodplains, wetlands and meadows, adding groundwater storage and summer base flow
• can turn a stream below a pond from ephemeral (not flowing year-round) to perennial

Where the beavers went

Before European contact, North America likely held 60 million to 400 million beavers. Early written records suggest most small and medium rivers were not single channels but braided with logjams and beaver dams, forming ponds, pools and floodplain wetlands. The fur trade and habitat loss cut them down; today about 10–15 million live in North America, and their numbers are generally growing. But where beavers are absent, people build BDAs to get the same benefits.

The Rio de las Vacas test

The dams' effects are well studied, but few studies measured conditions before building, so their value against changing precipitation is unclear. The USGS — with the Mountain Studies Institute, Rio Grande Return and the U.S. Forest Service — is using the Rio de las Vacas, a small meandering stream in the Jemez Mountains that peaks with late-spring snowmelt and can go dry in late summer, as a case study:

• In 2024, sensors went in at eight points to track streamflow, base flow, runoff, temperature and stream metabolism (a measure of ecosystem productivity and health).
• In 2026, multiple BDAs are being built along several miles of stream.
• Flights by uncrewed aircraft will track changes in floodplain vegetation and topography; the videos are in a USGS data release.

Justin Nichols collecting field measurements along the Rio de las Vacas, December 2025. Photograph by David Moeser, U.S. Geological Survey

The questions: Can "acting like a bunch of beavers" bring back historical summer flows? Can linked ponds shift reliance from snow to rain while improving ecosystem health and downstream water? And how does base flow change over time as BDAs go in?

Sources

Based on David Moeser, Benjamin Linhoff, Justin Nichols and Jake Kurzweil, Beaver Dam Analogs as Nature-Based Solutions to Mitigate Snowpack Loss in Northern New Mexico, U.S. Geological Survey Fact Sheet 2026–3019; a work of the United States government in the public domain.