Lake
Silfra Fissure
Silfra Fissure water temperature is currently Cold. Cold water ahead. Cold shock is a real risk on entry. Limit your time in. Located in the Sub-Arctic climate zone, it is currently summer. A smoothed air average of 10°C over recent weeks means the lake surface is firmly cold. Wetsuit strongly recommended. Cold shock is a real risk on entry.
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Community temperature reports are the most reliable local data.
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7-Day Forecast
6.9°C
High 10.7° / Low 9.4°
Cold conditions, a wetsuit is advisable
9°C
54cm depth
Cool ground, moderate baseline temperature
Weak
0 W/m²
Very little sunshine, minimal surface warming
24 km/h
S, gusts 43
Moderate S wind, some surface cooling and chop
5.6°C
Feels like wet
Cool on exit. Get dressed quickly, especially in the wind.
34.4 mm
7-day total
34mm of rain in the last 7 days. Lake inflows may have cooled and clouded the water.
Model estimates. Always assess the water yourself before entering.
Frequently asked questions
How is the lake water temperature estimated?
Lake temperature is estimated using exponential smoothing of 60 days of air temperature data, based on Kettle et al. (2004). The algorithm accounts for lake thermal mass. Larger lakes respond more slowly to air temperature changes. This is not a direct measurement; accuracy is approximately plus or minus 2 to 3 degrees C.
What do the temperature categories mean?
Each category covers a 4 degree C band: Warm (20 degrees C or above, no wetsuit needed), Comfortable (16 to 20 degrees C, most swimmers fine), Cool (12 to 16 degrees C, wetsuit optional), Cold (8 to 12 degrees C, wetsuit recommended), Very Cold (4 to 8 degrees C, wetsuit essential), Ice Risk (below 4 degrees C, experienced swimmers only).
What is the geographic zone?
The zone is derived from the lake's latitude and altitude. It reflects the climate regime: temperate zones have the highest model accuracy; alpine and equatorial highland zones have reduced accuracy due to solar heating effects not fully captured by air temperature data alone.
What is the swimmer exit temperature?
The exit temperature uses the Steadman (1984) apparent temperature formula, which accounts for wind speed and humidity on wet skin. Exiting water in wind with wet skin causes significantly faster heat loss than the air temperature alone suggests, especially at speeds above 20 km/h.