DATASHOAL // STATE OF THE BAY
Humboldt Bay
Week ending Sep 6, 2026Aug 30 – Sep 6
This week at a glance
HAB (harmful-algae) sampling 11 d old
Bottom line for the bay this week: Warm water pushing Vibrio to escalate and a domoic-acid signal in the phytoplankton are the two things shaping Humboldt Bay this week, so keep close to your certified-area status and CDPH advisories.
About this report
State of the Bay is decision support, not a harvest notice. It distills varied ocean, river, and sampling data into a weekly read on your bay; closures are set by the appropriate public health regulator, which does not endorse this report, so confirm your certified-area status with that agency before harvesting. Narrative text is generated by an AI model from documented measurements, available on request. Spot an error? austin@datashoal.io.
Growth conditions
Suboptimal conf moderateOBSERVED 57.3 °F (14.1 °C) ▲1.1 °F vs prior 4 wk ▼1.1 °F vs last yr chl-a 4.4 mg/m³
Conditions for oyster growth were suboptimal this week. Water temperature averaged about 14.7 °C with salinity around 34 and chlorophyll-a near 4.4 mg/m³, so food availability was reasonable but the thermal side kept growth below its best. Water temperature ran a touch warmer than the preceding four weeks but about 0.6 °C cooler than the same week last year.
Watch: A steady climb in water temperature back toward the roughly 20 °C spawning range, paired with holding chlorophyll-a, would move growth conditions out of the suboptimal band.
Rainfall closure risk
Low conf highOBSERVED 119.24 ft³/s ▼0.9 ft³/s vs prior 4 wk provisional
River discharge into the bay was low this week. Flow averaged lower than the preceding four weeks and well below the same week last year, so freshwater inflow stayed below baseline. The gauge reading is still provisional.
Watch: A sharp jump in combined Mad River and Eel River flow after a storm would be the first sign of a runoff spike.
Biotoxin early warning
Elevated stale · last sample Aug 26 (11 d)EARLY WARNING PSP: not signalled DA: signalled DSP: not signalled (stale)
Toxin-producing phytoplankton risk was elevated. Pseudo-nitzschia is blooming, signalling the domoic-acid (amnesic shellfish poisoning) pathway, while Alexandrium (paralytic shellfish poisoning) and Dinophysis (diarrhetic shellfish poisoning) were examined and not signalled at this sampling. The latest harmful-algae (HAB) sample is about a week and a half behind, and closure-grade tissue toxin levels remain CDPH's call, not measured here.
Watch: Newer sampling showing Pseudo-nitzschia intensifying, or Alexandrium or Dinophysis starting to appear.
Vibrio early warning
Escalate conf highOBSERVED 60.7 °F (15.9 °C) daytime avg in season June 1 - September 14
Vibrio early-warning conditions were at escalate, and the bay is inside its control season of June 1 to September 14. The month's average daytime water temperature was about 15.9 °C, or 60.7 °F, above the 60 °F escalate mark. That is warmer than the same week last year. Vibrio harvest controls are CDPH's determination, not this report's.
Watch: Daytime water temperature holding above the 60 °F escalate mark or climbing further.
Sanitary closure risk (fecal coliform)
Indeterminate not measuredNOWCAST not measured surrogate: river inflow 119.24 ft³/s provisional
Growing-area (fecal-coliform) status is not directly measured in this Phase-1 report and remains indeterminate. DataShoal does not assay fecal coliform, so the low river-discharge signal stands as the interim surrogate this week. CDPH under the NSSP is the classification authority.
Watch: A rise in the river-flow surrogate after rainfall is the early cue that growing-area conditions may be shifting.
The data behind this report
| Source | Data family | Freshness |
|---|---|---|
| Bay water-quality sensor | in-bay sensor | current · Sep 6 |
| River flow gauges | river gauge | current · Sep 6 |
| HAB (harmful-algae) sampling | plankton | stale · last sample Aug 26 (11 d) |
| Heat stress index | planned · not in this report | |
| Seven-day outlook, all indicators | planned · not in this report |