When it comes to managing water in uncertain times, few things are more important than knowing how much is flowing in the river alongside your city, or filling the reservoir that irrigates local farms.

That information is crucial to deciding how much water is available to irrigate crops, whether to declare a flood emergency or whether to launch a lazy rafting excursion.

But this basic information is at risk across the West because the nation lacks a reliable funding source for the simple stream gages that measure river flows. The United States Geological Survey, which handles most stream monitoring across the country, must rely on annual appropriations by Congress to maintain its network of stream gages.

As a result, dozens of gages across the West are at risk of being shut down every year. This network of is already considered too thin in most states, leaving huge gaps in streamflow data in areas of critical habitat or serious flood risk.

“The USGS does not have a line item in the federal budget to use at our discretion for stream gaging,” said Kirk Miller, a supervisory hydrologist at the agency’s Wyoming-Montana Water Science Center. “When you start talking about life and property hinging on access and timeliness of the streamflow data, it’s pretty important.”

The USGS operates about 8,200 stream gages across the country at an annual cost in 2016 of $184 million. That works out to an annual average of about $16,300 per gage.

Many also gather other kinds of important data, such as water temperature and specific water quality information. These days, many gages upload their data automatically every 15 minutes via satellite link.

Stream gages typically track water elevation and then use calculations to convert that into data on streamflow volume. This illustration shows one example of a stream gage that uses pressurized gas to measure water elevation. (Image Courtesy US Geological Survey)

There are 68 gages around the nation currently at risk of being shut down. An additional 131 were recently discontinued because of funding shortfalls. Some had been gathering streamflow data for decades, representing the death of an important environmental record. At an average annual cost of $16,300 per gage, it would cost just $2.7 million annually to keep these devices running.

Stream gages are simple devices that measure water flow, usually by translating water elevation measurements into volume and speed data. If you see a tiny silo-like building beside a stream, or a metal box with a solar panel and a spiky antenna attached, it’s probably a stream gage.

The USGS is the primary agency that installs and maintains the gages, and also manages the troves of data they generate. The data is available online, where it is tapped by a wide variety of other government agencies and private entities.

The National Weather Service relies on USGS gages to inform the public about flood risk. State and federal agencies use the data to track snowmelt, which is crucial to planning water distribution and managing reservoir operations. Agencies of all kinds depend on the gages to know how much water is available to share among farms and urban water treatment agencies and to keep fisheries healthy.

Many scientists need an unbroken record of streamflow data to track environmental changes. Miller also cited the need for accurate information for developers building homes and businesses near floodplains. The size and location of floodplains can change over time, depending on weather and shifting climate conditions.

“People want to build riverfront property, right?” Miller said. “That’s everybody’s dream. But if you’re building in a floodplain, that’s not a good thing, How do you define the floodplain? That’s what you can hope to do with a longer-term record.”

The problem is not limited to maintaining existing stream gages; many areas need more of them.

In California, the recently concluded five-year drought highlighted shortcomings in the state’s stream gage network.

A recent report by the Public Policy Institute of California (PPIC) revealed that about half the watersheds identified as critical aquatic habitat in the state have no stream gages at all. That made it impossible to manage water rights during the drought to ensure enough water was left in streams for fish and other wildlife.

A USGS technician inspects a stream gage on the South Fork Boise River, near Featherville, Idaho, during heavy runoff on May 8. The next day, the Boise River saw its highest flows in 106 years of recordkeeping. Some gages can be treacherous to access during high flows, such as this one, which is reached by an aerial cableway connected across the river via the metal tower on the right. (Photo Courtesy USGS Idaho Water Science Center)

“In watersheds where they didn’t have that stream gage information, they couldn’t really act,” said Henry McCann, a research associate at the PPIC and co-author of the report. “California just didn’t have stream gages in the right places from the environmental perspective.”

According to the USGS, 12 stream gages in California are considered threatened by funding problems, and two were recently discontinued.

The nation lost dozens of stream gages in 2013 as a result of sequestration – the procedure created by Congress to force spending cuts if members cannot reach a deal to reduce the national debt.

“Ever since sequestration started a couple years ago, we’ve lost about four or five gages, and there are a couple more that are potentially on the chopping block,” said Kevin Bazar, a hydrographer with the USGS Truckee field office. “We have hardly any around Lake Tahoe any more.”

Costs vary widely to operate stream gages depending on local climate. A gage in Alaska, for example, costs a lot more to operate than one in Pennsylvania. Besides the challenges of remote sites and periodic freezing conditions, gages must be inspected and tested in the field periodically; sometimes parts need replacing and the data they produce must be monitored, quality-checked and presented in a useful format.

“It’s very useful to know how much water is in there,” Miller said. “We have to make sure it’s the best it can be, because people are making decisions based on that data.”