About Neptune / 01
How Neptune Works
Neptune forecasts the chance of elevated bacteria at your beach: today, and for the next three days.
No water testing kit, no lab. Just the official sampling record, the conditions driving the ocean right now, and a model that has learned how the two fit together.
Why a forecast helps
Official testing is the ground truth, and Neptune would not exist without it. But it has a gap built into it: samples are typically collected about once a week, and the lab needs another 24 to 48 hours to grow and count what is in them.
So the number posted today describes water that was scooped up days ago. In between, it rains, tides turn, and swells arrive. That is the space a forecast fills.
The process
- 01
Learn from years of lab results
Neptune starts with the official record: years of Enterococcus samples collected and tested by the agencies that monitor these beaches. That history is what teaches the model how a beach behaves.
- 02
Add what the ocean is doing now
Rainfall, tides, waves, river discharge, sunlight and water temperature all shift how bacteria move and survive. Neptune pulls the current readings for each beach and feeds them in alongside the history.
- 03
Estimate the chance of an exceedance
A machine-learning model weighs those conditions against what it learned and produces one number per beach: the chance that bacteria exceed the applicable safe-swimming threshold, 104 MPN/100mL for ocean water.
- 04
Publish it, then check the homework
That estimate becomes the Neptune Index you see on the board. When the next official lab result arrives, Neptune compares it against what it predicted for that day, so the track record is visible rather than asserted.
What the risk levels mean
The Neptune Index is a percentage. It is our model’s estimated probability that Enterococcus exceeds 104 MPN/100mL at that beach. A lower percentage means an exceedance is less likely. A higher percentage means it is more likely.
- 0–29%Low bacteria levels
- 30–49%Moderate bacteria levels
- 50–74%High bacteria levels
- 75–100%Very high bacteria levels
Those labels come from the relationship we see in the record. When past forecasts are lined up against the official lab results that followed them, samples predicted in the lower ranges have tended to come back with lower bacteria levels, and samples predicted in the higher ranges have tended to come back higher.
So the labels describe a likelihood, and how that likelihood has borne out. They are not measured bacteria counts, and no reading here is a measurement of the water you are standing in.
A Low reading means conditions look unfavorable for high bacteria, not that the water has been tested and cleared. A High reading is a reason for caution, not a closure. Official advisories and closures take precedence over anything on this page.
Forecast vs. lab test
These answer different questions, and it is worth knowing which one you are reading.
A lab test
What the agencies do
- Measures a real water sample
- Tells you about one spot, at the moment it was collected
- Takes 24–48 hours to come back
- Usually taken about once a week
A Neptune forecast
What this site does
- Estimates, using conditions and past results
- Covers today and the next three days
- Updates once a day
- Never touches the water
One measures the past precisely. The other estimates now and next. You want both.
How to use it
Find your beach
Tap it on the map, or find it in the list.
Read today, then the days ahead
Today’s band tells you what Neptune expects right now. The three-day outlook is for planning the weekend.
Check the official notice before you get in
Always. A posted advisory or closure overrides anything on this page.
Questions
What is Enterococcus?
A group of bacteria that lives in the guts of people and animals. It is hard to test seawater for every germ that might make you ill, so agencies test for Enterococcus instead and use it as an indicator: more of it suggests a greater chance that sewage or runoff has reached the water. Finding it does not identify any particular illness or organism. It is a signal worth paying attention to, not a diagnosis.
Does Neptune collect its own water samples?
No. Neptune does not sample, test, or measure water. Every lab result it learns from was collected by an official monitoring program. What Neptune adds is a forecast between those tests, built from that record plus current conditions.
Does this replace official advisories?
No, and it is not meant to. A posted closure or advisory comes from people who sampled that water and have the authority to act on it. Neptune is an estimate. If the two ever disagree, the official notice is the one that counts. Check it before you get in.
Why does the forecast change?
Because the ocean does. A day of rain, a big swell or a spring tide can all move the estimate, and Neptune recalculates once a day with the latest conditions. A beach that read Low yesterday can read Moderate today.