Neptune Index
Manhattan Beach - 28th St
Low bacteria levels
Predicted to be below the EPA swimming threshold today.EPA swimming thresholdThe EPA's safe-swimming limit for ocean water is 104 MPN/100mL, the most probable number of bacteria per 100 milliliters. Readings above this are classified as an exceedance, meaning bacteria levels are unsafe for swimming.
7-Day Window
- 0–29%
- Low bacteria levels
- 30–49%
- Moderate bacteria levels
- 50–74%
- High bacteria levels
- 75–100%
- Very high bacteria levels
Top contributing factors
- 1.Hours since high tidemaking water quality cleaner•The time since high tide has given the water a chance to clear itself.
- 2.High tide levelmaking water quality cleaner•The high tide is not reaching far enough up the sand to stir bacteria loose.
- 3.Air temperaturemaking water quality cleaner•Cooler weather makes it harder for bacteria to survive.
Latest Lab Sample Result
September 29, 2026 · 5 MPN/100mL, below the EPA safe swimming limit of 104
Taken 4 days ago
Our daily forecast matched the official lab result in 7 of the last 7 samples.
Tap a dot for details.
A match means our risk call agreed with whether the lab result was above or below the EPA threshold of 104 MPN/100mL.
Frequently asked questions
Project Neptune is an ocean water quality forecasting platform for beaches. We predict the probability that a beach will exceed safe bacteria levels before it happens, so beachgoers and municipalities can make informed decisions in real time rather than waiting days for lab results.
We use a machine learning model trained on historical water quality data combined with live environmental inputs: rainfall, wave conditions, river and storm-drain flow, tides, and ocean data from sources like NOAA, USGS, and CDIP. The model learns the patterns that typically precede high-bacteria days and estimates the likelihood of an exceedance.
We test for enterococcus. While we do not physically test ourselves, we utilize 30 years of historical data to power our predictions. Enterococcus samples have been collected at U.S. coastal regions since 1997, when the EPA Beach Act went into effect. The Act requires coastal municipalities, usually counties, to collect water samples from beaches on a weekly basis.
Each sample is processed in a lab for 24 to 48 hours, then posted to a web platform that feeds back to the EPA. It's a solid system for regulatory compliance, but it falls short on user experience. The data is hard to access, and by the time a beachgoer sees it, it's already stale for deciding whether to go in the water.
Enterococcus is the fecal indicator bacteria widely accepted as the standard for measuring ocean contamination that can make people sick. Think: trace presence of feces in the water. Enterococcus itself isn't harmful, but it signals the likely presence of other pathogens, like staphylococcus, that can cause illness.
Our model is evaluated on its ability to distinguish safe from unsafe days, and it performs well on that measure, but no forecast is perfect. We're transparent about accuracy and continually validate predictions against real measured results. Project Neptune is a decision-support tool, not a substitute for official advisories or your own judgment.
Lab lag is the multi-day delay between when a water sample is taken and when results are available. During that window, beaches can be open with dangerous water, or closed when the water has already cleared. Our model is built specifically to address this delay.
Swimming in water with elevated bacteria is associated with gastrointestinal illness, skin rashes, and ear, eye, and respiratory infections. Decades of public health research have linked higher fecal-indicator bacteria levels to higher rates of swimmer illness. Children, the elderly, and people with weakened immune systems face greater risk.
No. Project Neptune complements official monitoring; it does not replace it. If a government agency has posted a closure or advisory, follow it. Our goal is to give you better information faster, especially in the gap between lab samples.