Estimated surface temperature for Big John Flat in Beaver County, Utah, updated with live National Weather Service air temperatures and a seasonal model tuned to this lake's latitude and depth. Use it to plan fishing, swimming, and boating — then verify on the water.
Water temperature
Modeled surface-temperature estimate built from seasonal climate, lake depth, and live National Weather Service air temperatures near this lake.
Seasonal estimate. Checking current National Weather Service air temperatures…
Warmest water of the year. Fish hold deeper or feed in low light; swimming and watersports are at their best.
| Month | Typical surface temp | Conditions |
|---|---|---|
| January | ~43°F | Frigid |
| February | ~42°F | Frigid |
| March | ~46°F | Cold |
| April | ~54°F | Cold |
| May | ~64°F | Cool |
| June | ~73°F | Warm |
| July | ~79°F | Peak summer |
| August | ~80°F | Peak summer |
| September | ~76°F | Peak summer |
| October | ~68°F | Warm |
| November | ~58°F | Cool |
| December | ~49°F | Cold |
Estimates are modeled, not measured. Actual temperatures vary with depth, wind mixing, and recent weather — verify conditions before swimming, boating, or heading onto ice.
Water temperature FAQ
LakeList currently estimates the surface temperature of Big John Flat at about 80°F (peak summer). This is a modeled estimate from seasonal climate, lake depth, and National Weather Service air temperatures — actual readings vary by day, depth, and location on the lake.
Surface temperatures at Big John Flat typically peak in August, reaching around 80°F in an average year. Shallow bays warm faster than the main basin, so mid-summer readings can run a few degrees higher near shore.
Big John Flat typically stays open through the winter — modeled surface temperatures rarely reach lasting ice cover. Cold snaps can still produce shoreline ice, so check local conditions in winter.
LakeList models the seasonal surface-temperature cycle from the lake's latitude and depth, then adjusts it with current National Weather Service air temperatures near the lake. Deeper lakes warm and cool more slowly than shallow ones, so the model lags and dampens the air-temperature cycle accordingly. Treat it as a planning estimate, not a measured reading.