Lac du Bourget Water Temperature Today
France's largest natural lake, warm and sheltered near Aix-les-Bains.
In August Lac du Bourget averages about 24°C at the surface, peaking near 24°C in July, August, September and dropping to roughly 7°C at its coldest.
Lake surface temperatures are modelled from long-term monthly averages and refined with live air temperature, wind and UV. Sea temperatures elsewhere on SwimTemperature come from measured marine model data.
Lac du Bourget water temperature by month
| Month | Average water temperature | Swimming |
|---|---|---|
| January | 8.1°C | cold |
| February | 7.0°C | cold |
| March | 8.1°C | cold |
| April | 11.3°C | cool |
| May | 15.5°C | mild |
| June | 19.8°C | mild |
| July | 22.9°C | warm |
| August | 24.0°C | hot |
| September | 22.9°C | warm |
| October | 19.8°C | mild |
| November | 15.5°C | mild |
| December | 11.3°C | cool |
Lac du Bourget swim conditions FAQ
Best time to swim, water safety and the temperature thresholds that matter for open-water swimming in Lac du Bourget.
Best time to swim
The warmest water in Lac du Bourget is in July, August, September, around 24.0°C.
The comfortable swim season — 18°C or warmer — covers June, July, August, September, October. Right now (August) expect about 24.0°C.
Within a day, the surface is warmest in the late afternoon, while early morning is calmest and quietest for boat traffic.
Water safety tips
- Enter Lac du Bourget slowly and let your breathing settle before swimming out — cold shock is the biggest single risk in fresh water.
- Swim parallel to the shore rather than out and back, so you are never far from a safe exit.
- Lakes have no lifeguard on most shorelines: swim with a partner and use a bright tow float so boats can see you.
- Check for boat traffic, sudden drop-offs, weed beds and submerged obstacles before your first swim of the season.
- Deep lakes stay cold below the surface even in a heatwave — expect a sharp thermocline a metre or two down.
- After heavy rain or during a warm calm spell, avoid swallowing water: runoff and algal blooms can cause illness.
- Get warm and dressed quickly after cold swims — afterdrop peaks 10–30 minutes out of the water.
Temperature thresholds
| Water | Feels | What to do |
|---|---|---|
| 24°C and above | Warm | Comfortable for long swims in swimwear. Watch UV and stay hydrated. |
| 20–23°C | Pleasant | Ideal open-water conditions for most swimmers; no neoprene needed. |
| 18–19°C | Fresh | Fine for 30–60 minutes; a shorty wetsuit extends comfort. |
| 14–17°C | Cool | Cold-water rules apply. A 3/2mm full suit is sensible. |
| 10–13°C | Cold | Limit to short swims, 4/3mm suit, gloves and boots; never swim alone. |
| Below 10°C | Very cold | Cold shock and swim failure risk. Acclimatised swimmers only, minutes not hours, with supervision. |
At today's estimate of 24.0°C, Lac du Bourget rates as hot — Excellent.
What is the water temperature of Lac du Bourget right now?
In August the surface of Lac du Bourget averages about 24°C. The reading at the top of this page refines that monthly average with today's live air temperature, wind and UV.
Can you swim in Lac du Bourget?
Yes. Lac du Bourget reaches 18°C or warmer in June, July, August, September, October, which most swimmers find comfortable without neoprene. Outside those months treat it as cold-water swimming.
When is the best time to swim in Lac du Bourget?
July, August, September offer the warmest water, around 24°C. Within the day, late afternoon is usually warmest at the surface, while early morning is calmest with the least boat traffic — the usable swim season runs across June, July, August, September, October.
How cold does Lac du Bourget get in winter?
The coldest month averages roughly 7°C at the surface. At that temperature cold shock is a genuine hazard for unacclimatised swimmers.
What water temperature is safe to swim in?
Above 20°C is comfortable for most people, 18–20°C is fresh but fine for shorter swims, 14–17°C calls for a wetsuit, and below 10°C is experienced cold-water swimmers only — minutes rather than hours, always with someone watching.
Do I need a wetsuit in Lac du Bourget?
Based on the monthly averages: no wetsuit needed at 22°C or above, a shorty from about 18°C, a 3/2mm full suit from 14°C, and 4/3mm with gloves and boots below 14°C. Lac du Bourget peaks near 24°C and bottoms out near 7°C.
Is Lac du Bourget safe to swim in?
Most of the year, yes, provided you pick a known entry point, swim parallel to the shore with a partner, and check local signage. Avoid swimming after heavy rain or during visible algal blooms, and remember lake shorelines are rarely lifeguarded.
Compare lake temperatures
Pick up to 4 lakes to compare today's water temperature and the next seven days.
| Lake | Today | Next 7 days |
|---|---|---|
| Lac du BourgetFrance | 24.0°Chot | Loading forecast… |
| Lac du BourgetFrance | 24.0°Chot | Loading forecast… |
| Lac d'AiguebeletteFrance | 25.0°Chot | Loading forecast… |
Water temperatures are modelled from long-term monthly averages for each lake and refined daily with forecast air temperature, so the seven-day column shows the expected trend rather than a measured buoy reading.
Open the full lake comparison tool · See Lac du Bourget on the live lake temperature map
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