Reading the Dashboard
A plain-language guide to interpreting salmon population data, understanding what the numbers mean, and knowing when to be cautious about what the data can and cannot tell you.
Where the Data Comes From
The Salmon Health Dashboard uses data from two main sources:
Salmon Return Data — WDFW SPI Database
The Washington Department of Fish and Wildlife maintains the Salmonid Population Indicators (SPI) database, which tracks escapement and abundance estimates for salmon populations across Washington state. "Escapement" means the number of adult fish that escape the fishery and make it back to spawn. Data is collected annually by WDFW biologists and tribal monitors using a combination of snorkel surveys, weir counts, carcass surveys, and mark-recapture methods.
Stream Temperature — USGS NWIS
The U.S. Geological Survey operates hundreds of stream gauges across Puget Sound that record water temperature (and streamflow) every 15 minutes. The dashboard pulls the most recent temperature reading from nearby stations for each watershed. These are real-time measurements, not estimates.
How fresh is the data? Salmon return estimates are updated annually — typically after WDFW processes the previous year's survey data. Stream temperatures are refreshed every 15 minutes from live USGS gauges. The dashboard shows timestamps so you always know when data was last updated.
Understanding Population Charts
The main chart on the dashboard shows annual salmon returns over time for a selected watershed and species. Here is how to read it:
Y-axis: Number of fish
The vertical axis shows the estimated number of adult fish returning to spawn in a given year. Higher is better. Note that the scale varies by watershed — a "good" year in a small watershed might be a fraction of a typical year in a large one like the Skagit.
X-axis: Year
Each data point represents one complete return year. Salmon have multi-year ocean cycles, so natural variation between years is normal. A single bad year is not necessarily a crisis; a long downward trend is.
Trend line
The shaded area or smoothed line shows the overall direction of the population. An upward trend over 10+ years is a positive signal. A downward trend of similar length is concerning even if individual years spike upward.
Recovery target line (where shown)
Some charts include a horizontal line showing the recovery target established in the Puget Sound Chinook Salmon Recovery Plan. Current populations are typically well below this target — reaching it is the long-term goal of coordinated recovery efforts.
What the Status Colors Mean
The map and watershed selector use color-coded status indicators. These are based on population levels relative to long-term baselines — not a single year's data:
Healthy
Population is at or near historical baseline and recovery targets. This is rare for Puget Sound Chinook.
Caution
Population is below historical baseline or showing a declining trend, but not in immediate crisis. Continued monitoring and habitat work is important.
Concern
Population is significantly below recovery targets or showing a steep multi-year decline. Urgent habitat and management action is needed.
Status colors are always paired with text labels — they are never the only indicator. If you are using a screen reader or viewing the site in grayscale, every status is still clearly labeled.
Reading Environmental Indicators
The basin detail pages include environmental indicator charts alongside the salmon population data. These provide context for why salmon populations change:
Water Temperature
Unit: °C or °F
Good range: Below 16°C (60°F)
Concerning: Above 20°C (68°F)
Salmon are cold-water fish. High temperatures reduce dissolved oxygen, increase disease susceptibility, and can be directly lethal to eggs and juveniles.
Streamflow
Unit: cubic feet per second (cfs)
Good range: Near or above historical median
Concerning: Well below historical median, especially in summer
Low flow concentrates fish in smaller areas, raises temperature, and can strand salmon on gravel bars. It also reduces the connectivity between spawning areas.
Data sources: Environmental indicator trend charts (annual temperature and stream discharge) use real data from the USGS NWIS Statistics Service — annual median values across active Puget Sound monitoring stations. Current temperature readings (shown as metric cards) are live real-time readings from the same USGS gauge network.
What the Data Cannot Tell You
Understanding data limitations is as important as understanding what the data shows. Be cautious about the following:
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One year does not make a trend
A single year with unusually high returns (often driven by favorable ocean conditions) does not mean a population has recovered. Look at 10+ year patterns.
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Survey methods vary by watershed
Some populations are counted with high precision (weirs, PIT tags). Others rely on visual surveys with higher uncertainty. Confidence intervals are noted in the WDFW source data but not always visible on dashboard charts.
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Watersheds are not independent
Ocean conditions, climate patterns, and policy decisions affect multiple watersheds simultaneously. A bad year for one watershed often correlates with bad years for others.
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The dashboard shows escapement, not total run size
Escapement (fish that return to spawn after the fishery) is what is measured. Total run size — including fish caught — is larger. Neither number fully captures juvenile survival or ocean survival, which are key to understanding long-term trends.
How to Use the Dashboard Effectively
- Start with the map. Select a watershed you care about — either by clicking the map polygon or using the dropdown selector.
- Look at the trend, not just the latest year. The 10–20 year trend line tells you far more than a single data point.
- Compare watersheds. Switch between basins to see which systems are healthier and why — look for patterns in geography, land use, and stewardship activity.
- Check the data sources. Every chart on the dashboard shows its source and data vintage. The expandable "Data Sources" section at the bottom of the dashboard page lists all sources and caveats.
- Connect data to action. For each watershed, the basin detail page links to stewardship projects operating in that basin. Numbers only make sense in the context of what is being done about them.
Key Takeaways
- ›Salmon return data comes from WDFW's annual escapement surveys; stream temperatures come from live USGS gauges.
- ›Look at multi-year trends, not single years — natural variation is high.
- ›Status colors (green/yellow/red) are always paired with text labels and reflect long-term population trends.
- ›Environmental indicators like water temperature and streamflow provide context for why populations change.
- ›The dashboard shows escapement (spawning adults), which is one important metric — not a complete picture of population health.
- ›Good data use means knowing the limitations, not just reading the numbers.
For Educators — Discussion Questions & Activities
Discussion Questions
- Why is it misleading to judge a salmon population based on a single year's data? What would you need to see to conclude a population is recovering?
- Why do different watersheds have different data quality? What would affect how precisely we can count salmon in a given stream?
- If you were a salmon recovery manager, which environmental indicator would you prioritize — water temperature or streamflow? Why?
- The dashboard shows escapement (adult spawners), not total population size. What other measurements would give a more complete picture?
Activities
- ›Trend analysis: Have students open the dashboard, select three different watersheds, and write a 2–3 sentence interpretation of each population trend. Then compare: which watershed looks healthiest? What questions does the data raise?
- ›Data source investigation: Visit the WDFW SPI database or USGS NWIS directly. How does the raw data compare to what is shown on the dashboard? What choices were made in transforming the raw data into the visualizations?
- ›Uncertainty exercise: If a salmon count has a ±20% uncertainty, draw the range of possible values for a given year on the chart. How does this affect your interpretation of the trend?
Standards alignment: NGSS Science and Engineering Practices (analyzing and interpreting data, using mathematics and computational thinking). CCSS Math MP.3 (construct viable arguments). WA Data Literacy Standards.