How our data works
Where every number comes from, how old it is, and the rules we follow.
How often it updates
The whole site rebuilds every hour. Each lake page shows the local time of the last update, and every water reading shows how old it is.
Our sources
- Weather, wind, and forecasts: Open-Meteo.com, which combines forecasts from national weather services. Data licensed under CC BY 4.0.
- Water temperature, Alpine lakes: Alplakes, run by Eawag, the Swiss Federal Institute of Aquatic Science and Technology.
- Water level and temperature, United States: USGS Water Data, from the U.S. Geological Survey's lake gauges. This includes Lake Mead and Lake Powell, where the gauges are run with the Bureau of Reclamation. The Bureau publishes the official figures for those two lakes.
- Great Lakes level and water temperature: NOAA Tides & Currents. Levels use the International Great Lakes Datum of 1985, the shared US and Canadian reference for the Great Lakes. Each lake's figure comes from one gauge on its shore, and wind can push the level up or down by a few centimetres across a lake.
- Water level, Texas and Elephant Butte: the Texas Water Development Board, which compiles readings from the USGS, the US Army Corps of Engineers, the Bureau of Reclamation, the IBWC and the LCRA. Daily values, provisional and subject to revision.
- Photos: contributors to Wikimedia Commons, used under open licences. The photographer and licence are credited on every page that shows their photo.
- Lake outlines and positions: Natural Earth, public domain. We use them to make sure each lake's weather point sits on the water, not on the shore.
Measurements and models
A measurement comes from a sensor in the lake. A lake model is a scientific simulation that calculates the water temperature from the weather, the lake's shape, and past measurements. Models from research institutes are usually within a degree or two of the real surface temperature, but they're still estimates. Every lake page tells you which one you're looking at.
Our rules
- Every number shows where it came from and how old it is.
- Nothing older than 48 hours is ever shown as today's value, or 4 days for sources that publish once a day.
- We hide water temperatures outside 0–40 °C, or that jump more than 5 °C in a day, until we've checked them.
- Every water level says what it measures, because a lake's height above sea level and a gauge reading are different numbers. We hide any surface elevation outside 1–15,000 feet, which means a broken gauge.
- When we don't have a reliable number, we say so instead of guessing.
- We store everything in metric units and convert for display, so both units always match. The °C / °F buttons at the top of every page switch temperatures, wind speeds, water levels and distances together, and your choice is remembered on your device.
How we judge "good for today"
These are rules of thumb, not safety advice. Wind is the sustained speed 10 m above the water; gusts are short peaks.
| Activity | What we look at | Good when |
|---|---|---|
| Swimming | Water temperature | 18 °C or warmer is pleasant, 22 °C or warmer is warm. Below 14 °C is wetsuit weather. |
| Kayak and paddleboard | Wind and gusts | Wind under 12 km/h and gusts under 20 km/h |
| Sailing | Wind and gusts | Wind from 6 to 25 km/h with gusts under 35 km/h |
| Windsurf and kite | Wind and gusts | Wind of 22 km/h or more, with gusts under 50 km/h |
If thunderstorms are forecast in the next 12 hours, we mark every activity as a no.
"Below normal for this date"
Where a lake has a long record, we compare today's level with the median for the same date across every year we have, using a three-day window either side so each date has enough readings. We only say what is normal when at least five separate years are available, and we show the range as well as the median, because a lake can be low and still be within its usual swing.
Found a mistake?
Email hello@lakedip.com with the lake's name and what looked wrong. We check every report.