You check the weather app. It says 75 degrees and sunny. Looks like a great day for a swim, right?
Maybe. But weather apps do not tell you about the 15-knot onshore wind kicking up two-foot chop. They do not mention that the tide is ripping out through a narrow channel. They do not flag that air quality has quietly drifted into the unhealthy range from a wildfire two counties over.
Open water swimming conditions are more complex than a temperature and a sun icon. That is why we built SwimScore.
A Single Number That Means Something
SwimScore is a 0-100 rating that tells you how good conditions are for swimming at a specific spot, at a specific time, for a swimmer like you. It synthesizes data from multiple sources, weighs it against the characteristics of the swim location, and adjusts for your ability level.
The scale is intuitive:
- 80-100: Excellent -- Conditions are ideal or near-ideal. Get in the water.
- 60-79: Good -- Solid conditions with minor factors to be aware of. Most swimmers will have a great time.
- 40-59: Fair -- Swimmable, but conditions are mixed. Experienced swimmers may enjoy it; newer swimmers should exercise caution.
- 20-39: Poor -- Significant condition concerns. Only for very experienced swimmers who understand the specific risks.
- 0-19: Not recommended -- Conditions pose serious risks. Stay on shore.
One number, but a lot of intelligence behind it.
Where the Data Comes From
SwimScore is only as good as its data, so we pull from the best sources available and keep them fresh.
Weather Data (Open-Meteo)
Wind is arguably the single biggest factor in open water swim quality, and most people underestimate its effect. SwimScore ingests detailed wind data including speed, gusts, and direction relative to the swim spot. A 12 mph wind blowing offshore creates completely different conditions than the same wind blowing onshore.
Beyond wind, we pull air temperature, precipitation probability, cloud cover, and thunderstorm risk. SwimScore will drop sharply when lightning is a factor, because there is no safe way to swim in an electrical storm.
Marine and Wave Data (Open-Meteo Marine)
For coastal and ocean swim spots, wave data is critical. SwimScore factors in significant wave height, wave period, and swell direction. Short-period wind chop is a very different challenge than long-period ground swell, and the score reflects that. Our guide to understanding water conditions explains how wave height, period, and direction combine to shape your swim experience.
Water temperature is also pulled from marine data sources when available. Cold water affects everything from comfort to safety, and its impact scales with swim duration.
Tidal Data (NOAA)
Tides transform coastal swim spots. A sheltered cove at high tide can become an exposed reef at low tide. A gentle bay can develop strong currents during tidal transitions. SwimScore incorporates NOAA tidal predictions to understand where a spot is in its tidal cycle and how that affects swimmability.
Tidal current strength is especially important for spots near inlets, channels, and river mouths where flowing water concentrates.
Air Quality
This one surprises people, but air quality matters enormously for swimmers. You are breathing hard during a swim, pulling large volumes of air deep into your lungs. If that air is carrying elevated particulate matter from wildfires, industrial pollution, or dust storms, the health impact is amplified compared to sedentary activity.
SwimScore monitors air quality index data and factors it into the overall rating. On high-AQI days, the score will reflect the respiratory risk even if every other condition looks perfect.
Spot-Type Awareness
A critical design decision in SwimScore is that it understands the difference between types of swim locations. The conditions that matter at an ocean beach are fundamentally different from those at an inland lake or a river swimming hole.
Ocean spots weight wave data, tidal currents, and marine conditions heavily. Wind direction relative to the coastline matters a great deal.
Lake spots focus more on wind-driven chop, water temperature, and air quality. Waves on lakes are typically shorter-period and choppier than ocean swell, and the score model accounts for that.
River spots prioritize flow rate and recent precipitation that might affect current strength. A river that is gentle at normal levels can become dangerous after heavy upstream rain.
This means a SwimScore of 72 at your favorite ocean beach and a SwimScore of 72 at a mountain lake both genuinely represent "good conditions," even though the underlying data and risk factors are completely different.
Personalized for Your Level
Here is where SwimScore moves beyond a generic conditions report.
Two swimmers looking at the same spot at the same time can see different scores, because SwimScore adjusts for ability level. When you set up your profile in SwimPass, you indicate your experience level, and the scoring model shifts its thresholds accordingly.
For a beginner, moderate wind chop might push a score from "Good" into "Fair" because the sighting and breathing challenges are significant for someone still building confidence. For an advanced swimmer, those same conditions barely register.
This is not about gatekeeping. It is about giving you an honest assessment of how these conditions will feel to you, specifically. A beginner who sees a score of 55 is getting a genuinely useful signal: you can swim, but be prepared for some challenge. An advanced swimmer seeing 75 for the same conditions knows it is a solid day out.
Training Context Modes
SwimScore also adapts based on what kind of swim you are planning. A casual dip has different requirements than a serious distance training session.
If you are heading out for a relaxed swim with friends, slightly choppy conditions might be a non-issue. But if you are trying to hit pace targets for an upcoming race, that same chop could meaningfully disrupt your training. SwimScore can reflect that context, helping you decide not just whether to swim, but whether to do the specific swim you had planned.
What SwimScore Is Not
We want to be clear about what SwimScore does not do. It is not a safety guarantee. No algorithm can perfectly predict the complexity of natural water environments. It is not a replacement for on-the-ground assessment when you arrive at your spot. And it is not a substitute for swimming skills, experience, and good judgment.
What it is: the most comprehensive pre-swim conditions check available, distilled into a format you can use in seconds. Think of it as a well-informed friend who obsessively checks every data source before every swim and gives you their honest take.
Why It Matters
Open water swimmers have always done some version of this assessment manually. Check the weather. Look at the wind forecast. Google the tide chart. Maybe check a surf report. If you want to sharpen that manual skill alongside using SwimScore, the best time of day to swim outdoors covers how wind, tides, and temperature shift through the day. Try to remember what AQI was doing.
SwimScore collapses all of that into a single glance. Not to oversimplify, but to save you the time and reduce the chance that you miss something important. The data is all still there if you want to dig into the details, but the headline number gives you an immediate, informed starting point.
Because the best swim is one where you knew what you were getting into before you got in.