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How Web Flags help the public understand our data

USGS Water Data are important to the public and help people to make critical decisions, but conditions in the field are often complicated to convey. Therefore, USGS hydrologic technicians apply web flags to convey gaps in data to the public so users understand unusual values or missing data.

Web flags are displayed graphically on monitoring location pages and can either be kept on data permanently or removed when data are reviewed and corrected. Here are some common web flags and some example reasons for their application. This list is not comprehensive and therefore does not include all possible web flags or all possible causes.

Web Flags Indicate Why No Data are Present



A station has been permanently or temporarily discontinued.

Example Causes

  • A study has ended and data no longer needs to be collected at that site
  • Funding has been discontinued
a screenshot of a hydrograph that has a grayed out portion reflecting no data over a period of time.

A hydrograph of temperature at site 13343000, where temperature data has been discontinued and is no longer served at this site.

Temporarily Unavailable


Data are not available and are not being transmitted for a short period of time, which can vary from hours to months, depending on site access.

Example Causes

  • Transmission issues with telemetry equipment
  • Issues with our data processing software



One or more types of data are not available because the station is in its off season, but data will be back in a matter of months.

Example Causes

  • Weather conditions may damage sensors (e.g., due to ice chunks in the river)
  • Accessibility changes that fluctuate with seasonal changes such as
    • Lack of water flow
    • Limited access to equipment
    • Lack of ability to telemeter data

Web Flags Tell Users to be Cautious With Data

Equipment Malfunction


We suspect or have evidence that there is an equipment malfunction.

Example Causes

  • Our monitoring equipment malfunctions, leading to inaccurate data
  • Our monitoring equipment has been damaged
a screenshot of a hydrograph that has a vertical blue lines indicating periods of no data.

A hydrograph at location 13307000 where web flags were applied during periods of malfunctioning equipment in November 2020.



Water that is backed up as compared with its normal or natural condition of flow. In stream gaging, a rise in stage is produced by a temporary obstruction. The difference between the observed stage and the one indicated by the stage-discharge relation is reported as backwater. Using the “Backwater” web flag allows users to see gage height data, but not discharge data as these data need to be corrected.

Example Causes

  • Obstructions, such as beaver dams, weeds, or vegetation
  • Ice jam in a stream channel
  • Flooding downstream of the stream gage
Photograph of a stream with pooled water, an example of a stream affected by backwater.

Photo of a stream affected by backwater. Photo credit, USGS-Scott Sylvester



Data are not being accurately transmitted due to the presence of ice.

Example Causes

  • In cold climates, streams are commonly affected by ice, which can
    • Inaccurately show more or less water than is actually there
    • Block sensors
    • Create backwater
  • Otherwise prevent data from being transmitted accurately
Phhotograph of a stream covered in ice, an example of a stream gage that would be ice-affected.

Photo of a stream whose data readings are affected by the presence of ice. This is when the ‘Ice Affected’ web flag would be used. Photo credit USGS-Austin Bove.



Maintenance is planned and/ or being conducted to stream monitoring equipment by our field hydrologic technicians. 

Example Causes

Monitoring equipment

  • Is damaged and needs to be repaired
  • Requires routine maintenance
  • Is currently undergoing maintenance
A photograph of two people repairing instrumentation on a stream bank. No data will be transmitted during this activity and a web flag can be applied to data during this time period.

Two USGS staff repair equipment at an active streamgage. No data will be transmitted during this activity and a web flag can be applied to data during this time period. Photo credit: USGS - Cory Rogaczewski.

This is not a comprehensive list of all web flags that may be applied, but these examples show how web flags help us to explain to users what is happening with our data. Users can quickly glance at hydrographs with web flags and understand why data may not be showing up, what current conditions are, and how reliable we believe current data to be. Data transparency is fundamental to our mission at USGS.