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How risk bands
are defined.

Each beach is assigned one of four risk bands derived from the model's calibrated exceedance probability — the chance that enterococcus exceeds the EPA single-sample threshold of 104 CFU/100mL on a given day.

From probability to label.

EPA STV

The single-sample threshold for enterococcus in marine waters is 104 CFU/100mL (EPA Recreational Water Quality Criteria, 2012). Exceeding this value does not guarantee illness but indicates elevated risk.

Calibrated probability

The model outputs a calibrated p_exceed — the estimated probability that the true concentration will exceed 104 CFU/100mL on the forecast day, given environmental covariates.

Band cut-points

Cut-points (15 %, 35 %, 65 %) are tuned so false negatives (missed High/Very High days) are penalised more heavily than false positives in the loss function, providing a conservative public-health posture.

County advisories

Shorelife bands are forecasts; official CDPH/county advisories are posted after a confirmed sample violation. A Very High forecast does not replace a posted advisory.

Four levels, calibrated for public health.

BandGuidanceProbability gateAction
Low
Low modeled risk
Lower modeled exceedance risk.
< 35 CFU/100mL
Predicted exceedance probability < 15 %
Lower modeled exceedance risk, but still check county advisories and posted warnings.
Moderate
Moderate modeled risk
Elevated modeled risk.
35–104 CFU/100mL
Predicted exceedance probability 15–35 %
Avoid swallowing water; rinse thoroughly after exit.
High
Elevated modeled risk
High modeled exceedance risk — check county advisories.
104–320 CFU/100mL
Predicted exceedance probability 35–65 %
Avoid water contact and check county advisories, especially for sensitive groups.
Very High
Very high modeled risk
Model estimates closure-level exceedance probability.
> 320 CFU/100mL
Predicted exceedance probability > 65 %
Avoid the water; expect closure-level concentrations based on recent samples and conditions.
Advisory
Official advisory posted
Authoritative county posting — not a model prediction.
n/a CFU/100mL
Set by the county — not a model output
Do not enter the water. The county has issued an active health advisory based on recent samples or an event (sewage spill, storm runoff). Follow the official county source for current status.

What the model can and cannot do.

  • 01Shorelife forecasts are probabilistic estimates, not certified sample results.
  • 02Official beach closures and advisories are issued by county environmental health agencies under California AB 411.
  • 03A Low band forecast does not mean safe water. Localised events (sewage spills, storm runoff) can override model predictions. This is a beta model estimate, not an official advisory.
  • 04The model is trained exclusively on marine enterococcus (culture-based, MPN/IDEXX). Freshwater E. coli and other analytes are outside its scope.
  • 05For confirmed regulatory status, always consult the current county health advisory for the specific beach.