Last updated May 28, 2026

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Fish & Wildlife Wetland Condition
WRMP Exhibit · Long-Term Monitoring

A Decade in Alviso Marsh

Fourteen years of monthly sampling in one tidal marsh at the southern edge of San Francisco Bay — the longest continuous fish-community record in the South Bay, and the prototype that shaped the WRMP network.

SBOTS · 2010–2024

The Laboratory at the Bay's Edge

For fourteen years, scientists have towed the same trawl through the same channels of Alviso Marsh. This is the longest continuous fish-community record in the South Bay — the SBOTS dataset — and it has quietly become the estuary's living laboratory.

14 yrsof monitoring Monthlysampling ~20stations 240+species observed
Space · Eco-cline

The Gradient You Can Taste

Walk the marsh from the wastewater outfall down to the open bay and the water changes under your boat — warmer and fresher upstream, saltier and oxygen-rich below. Fourteen years of trawls sort neatly into four station clusters, each with its own chemistry and its own cast of species.

ART 1 is its own cluster of one. The station just below the San José–Santa Clara wastewater outfall diverges from every other site in the marsh — its water chemistry and its fauna look like nowhere else.
Cluster fingerprints — water quality
Qualitative pattern from SBOTS WQ clusters — illustrative of direction, not measured values.
Time · Annual Cycle

Two Seasons, Not Four

California's Mediterranean climate gives the estuary a two-season pulse — wet winter into spring, then a long warm dry. Water quality sorts neatly into wet and dry. The fish see finer seasons than the thermometer does.

Winter and early-spring runoff pull anadromous and marine species upstream into Alviso's sloughs.

Time · Decade Scale

The Drought That Didn't End

After the 2014–2015 drought, the Alviso assemblage reorganized — and it has not returned. Those two years form their own cluster in the ordination: a short hinge between the old community and the new.

The wet years that followed looked nothing like the wet years before. The estuary kept breathing, but the rhythm had changed.

Transition (2014–15) Dry cluster Wet cluster
From Marsh to Network

Why This Shape of Program?

Everything Alviso has taught us is now built into the WRMP network's design.

Upstream–downstream eco-cline → stations stratified by position on the salinity gradient.

Two-season biology → at minimum two sampling events per year, tuned to the wet and dry pulses.

Regime-shift visibility → long-term monitoring, not one-off studies. You can only see a regime shift if you were already watching.

Alviso is the prototype. WRMP is the network.
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