Michelle's Oyster Weather Indicators
Early warning for harmful algal blooms & red tides in South African shellfish waters — from satellite chlorophyll & sea-temperature data.
Red-tide risk — check advisories before harvesting
High algal biomass consistent with a bloom / red tide. Shellfish may carry unsafe biotoxins (PSP / DSP shellfish poisons) — do not harvest for consumption without a laboratory biotoxin clearance. 3 sites showing rising algae. 2 not advised for harvesting right now.
🗺 Coastline at a glance
🎯 Where to source today
Saldanha Bay is not advised today. No site is clearly in the clear — check the cards below.
- 1KnysnaGarden RouteImproving — hold a few days
- 2St Helena BayWest CoastImproving — hold a few days
- 3⭐ Saldanha BayWest CoastPoor now — may improve
- 4Algoa Bay (Gqeberha)Eastern CapePoor now — may improve
Latest cloud-free chlorophyll pass: 30 Aug · Sea temp, waves, tide, wind & rain are live
Read this first.The algae reading comes from satellites that can't see through cloud, so it's the freshest clear pass — often a few days to a week or two old (worse in winter), never guaranteed “today.” That makes this a trend & early-warning tool. Each site shows its pass date and greys out when stale. For same-day confirmation before harvesting, the OCIMS red-tide tool is the authoritative check.
Saldanha Bay
West Coast
⭐ Michelle's main sourceSouth Africa's main oyster & mussel farming bay.
High chance of bloom conditions around 09-02 — treat as a red-tide watch.
- Algae now: Already in the Warning/Red band.
- Benguela wind: Upwelling-favourable wind — cold, nutrient-rich water at the surface.
- Wind outlook: Southerly / mixing winds ahead.
- Sea temperature: Cooling ~0.6°C.
- Sea state: Big waves will mix the surface.
A transparent blend of algae trend + wind + sea temperature — an estimate, not a lab result.
Most likely a Mixed diatoms bloom — usually not a toxin risk, but watch the oxygen if biomass is high.
Indicative prior from season + conditions + site history — not a species ID. Confirm with DFFE.
🛰 True-colour satellite view
NASA GIBS (VIIRS true colour) for the latest pass. Look for brown/red discolouration; cloud may hide the bay.
Southerly winds mixing the water — bloom risk easing.
St Helena Bay
West Coast
Classic Benguela red-tide zone — frequent blooms & rock-lobster walkouts.
High chance of bloom conditions around 09-02 — treat as a red-tide watch.
- Algae now: Already in the Warning/Red band.
- Benguela wind: Upwelling-favourable wind — cold, nutrient-rich water at the surface.
- Wind outlook: Southerly / mixing winds ahead.
- Sea temperature: Warming ~1.0°C over the window (stratifies).
A transparent blend of algae trend + wind + sea temperature — an estimate, not a lab result.
Most likely a Mixed diatoms bloom — usually not a toxin risk, but watch the oxygen if biomass is high.
Indicative prior from season + conditions + site history — not a species ID. Confirm with DFFE.
🛰 True-colour satellite view
NASA GIBS (VIIRS true colour) for the latest pass. Look for brown/red discolouration; cloud may hide the bay.
Southerly winds mixing the water — bloom risk easing.
Knysna
Garden Route
Home of the famous Knysna oyster.
Bloom risk stays low across the forecast window.
- Algae now: Low and stable.
- Wind outlook: Southerly / mixing winds ahead.
- Sea temperature: Cooling ~2.6°C.
- Sea state: Big waves will mix the surface.
A transparent blend of algae trend + wind + sea temperature — an estimate, not a lab result.
🛰 True-colour satellite view
NASA GIBS (VIIRS true colour) for the latest pass. Look for brown/red discolouration; cloud may hide the bay.
Southerly winds mixing the water — bloom risk easing.
Algoa Bay (Gqeberha)
Eastern Cape
Aquaculture Development Zone — mussels & oysters.
High chance of bloom conditions around 09-02 — treat as a red-tide watch.
- Algae now: Already in the Warning/Red band.
- Wind outlook: Southerly / mixing winds ahead.
- Sea temperature: Cooling ~1.4°C.
- Sea state: Big waves will mix the surface.
A transparent blend of algae trend + wind + sea temperature — an estimate, not a lab result.
Most likely a Mixed diatoms bloom — usually not a toxin risk, but watch the oxygen if biomass is high.
Indicative prior from season + conditions + site history — not a species ID. Confirm with DFFE.
🛰 True-colour satellite view
NASA GIBS (VIIRS true colour) for the latest pass. Look for brown/red discolouration; cloud may hide the bay.
Southerly winds mixing the water — bloom risk easing.
📜 Recent alert changes
- 01 SeptAlgoa Bay (Gqeberha)▲ Red-Tide Riskwas Warning · 8.9 mg/m³
- 01 SeptAlgoa Bay (Gqeberha)▼ Warningwas Red-Tide Risk · 5.9 mg/m³
- 01 SeptSt Helena Bay▼ Warningwas Red-Tide Risk · 6.5 mg/m³
- 01 SeptSt Helena Bay▲ Red-Tide Riskwas Warning · 15.0 mg/m³
- 01 SeptKnysna▼ Safewas Warning · 0.4 mg/m³
- 31 AugAlgoa Bay (Gqeberha)▲ Red-Tide Riskwas Warning · 8.9 mg/m³
- 31 AugKnysna▲ Warningwas Safe · 3.3 mg/m³
- 31 AugKnysna▼ Safewas Warning · 1.5 mg/m³
- 30 AugSt Helena Bay▼ Warningwas Red-Tide Risk · 6.5 mg/m³
- 30 AugSt Helena Bay▲ Red-Tide Riskwas Warning · 15.0 mg/m³
- 30 AugAlgoa Bay (Gqeberha)▼ Warningwas Red-Tide Risk · 5.9 mg/m³
- 30 AugSt Helena Bay▼ Warningwas Red-Tide Risk · 6.5 mg/m³
- 30 AugSt Helena Bay▲ Red-Tide Riskwas Warning · 15.0 mg/m³
- 30 AugSt Helena Bay▲ Warningwas Watch · 6.5 mg/m³
Over a season this shows how often each bay blooms, how long events last, and whether today is normal for the time of year.
📊 Bloom track record
How each bay has behaved since tracking began (05 Jul 2026) — a “bloom episode” is a spell in the Warning band or above.
- Saldanha Bay2 bloom episodes · typically ~0.2 days · longest 0.2done running now · 6d
- St Helena Bay5 bloom episodes · typically ~0.6 days · longest 26.1done running now · 3d
- Knysna4 bloom episodes · typically ~2.7 days · longest 4.3d
- Algoa Bay (Gqeberha)3 bloom episodes · typically ~5.7 days · longest 6done running now · 12d
Built from what the 6-hourly checker actually saw — honest hindsight, not a forecast. Recording official DFFE closures over time would let this measure how many days of early warning the algae signal gives before a bed closes.
🎯 Track record & accuracy
How well the alerts have matched reality — the tool's honesty check. It earns trust by keeping score.
No field observations logged yet. Record what you see at the water (colour, foam, dead fish, taste, any lab result) on the settings page, and this scoreboard fills in — the satellite then calibrates itself to the ground truth.
How to read this
Chlorophyll-a is the amount of algae in the water, measured from space by satellite ocean-colour sensors. When it climbs — and especially when it climbs fast— a phytoplankton bloom is building. Some of those blooms are toxic “red tides” whose biotoxins — the shellfish poisons PSP (paralytic), DSP (diarrhetic) and ASP (amnesic) — build up in oysters, mussels and other filter-feeders, making them unsafe to eat until the toxins clear.
A rapid rise (currently +50% over baseline) bumps the alert up a level even before the water is technically “high” — the goal is to catch a bloom while it's still building. These ranges are adjustable on the settings page.
Beyond the algae — the other warnings
- Harvest verdict — the green/amber/red call at the top of each card, combining algae, rain runoff and water temperature into one plain answer.
- Runoff — heavy rain washes bacteria and freshwater into growing waters; beds often close after big rain even with no red tide.
- Vibrio— warm water (≈18°C+) lets these bacteria build up in raw oysters; when it's high, cook rather than eat raw.
- Upwelling — southerly winds pull up cold, nutrient-rich water; when they relax the sea warms, stratifies and blooms can build.
- Tide & moon — spring tides (near new/full moon) flush growing waters harder than neap tides.
- ◌ Modelled value— NOAA's gap-filled product statistically estimates the algae level under cloud, so it runs near-daily where the real observations lag. It's a model, not a measurement — it bridges the gap on the chart but never sets the alert level.
- Official DFFE status— the shellfish-sanitation classification of each harvesting area (Class A: direct harvesting · B: depuration first · C: relaying). There's no public feed, so it's recorded by hand on the settings page with the date it was last checked.
Before you harvest — check the officials
This dashboard is an early-warning screen, not a food-safety clearance. For South African waters, confirm against the authoritative red-tide & biotoxin monitoring: