Lake Annecy water temperature today: the official reading, and why four websites give four figures
Today's official reading, taken from the sailing club's probe and refreshed on this page at every visit, then why four websites give four different figures for the same lake: a measurement, a model, an estimate and a private weather station.
The tourist office's official reading is 22.5°C on 15 September 2026, measured at the SRV Annecy sailing club. This figure is fetched from the tourist office at every visit to this page. For a sense of the season: in mid-September 2026, the same probe still read 23.4°C on 12 September 2026.
Type the same question into a search engine and you will get other figures, sometimes four degrees lower, for the same week. This page explains where each value comes from, and which one to trust before you get in the water.
What is the water temperature today?
The only institutional measurement published every day is the one from the Lake Annecy tourist office, on its weather page. It comes from a probe at the sailing club, on the Annecy shore, and can be read on both the French and the English versions of the tourist office website.
Today's reading, fetched from the tourist office at every visit: 22.5°C on 15 September 2026. If the tourist office does not respond, the page shows the last known reading with its date, and the tourist office weather page is the reference.
This figure describes the surface, close to the shore, in Annecy. It says nothing about the small lake to the south, or about the water ten metres down, which stays at 6 to 8°C all year. Ranges month by month are in the lake temperature month by month.
Why do websites show different temperatures?
Over a three-week window at the end of summer 2026, four sources gave four values for the same lake.
- Measurement: 23.4°C on 12 September 2026 at the sailing club probe, published by the tourist office.
- Live website: 22.9°C on 12 September 2026 from a private weather station, with no description of the method.
- Model: 21.9°C on 21 August 2026 on a website that calculates the temperature from weather data, without a probe in the water.
- Local estimate: 19.7°C at Talloires on 6 September 2026 on the same website, for a page per village.
Gap between the highest and the lowest value: 3.7°C. None of these sources is lying, they simply do not measure the same thing. A probe records real water at a precise spot; a model produces a theoretical average for a whole body of water.
The practical rule: a temperature without a place and a time is worthless. Look for the name of the station and the date of the reading. If they are missing, it is a calculation.
Where is the water warmest on the lake?
No source publishes beach-by-beach readings. The only institutional probe is in Annecy. The village pages of the aggregator websites are estimates, as the Talloires gap above shows.
What geography tells us: the small lake, to the south, is shallower than the main lake and warms up faster in spring. Enclosed, shallow bays get warmer in the afternoon than a quay exposed to open water. The depths of the two basins are in the depth of Lake Annecy.
Below about fifteen metres, the temperature no longer moves: 6 to 8°C in every season. Divers call this the thermocline, and it is the reason for the advice to get into the water gradually.
A base by the water settles the question of timing: you swim when the probe goes up, not when a parking space comes free. The search for places to stay in Annecy can be filtered by distance to the lake before you compare prices.
See places to stay near the lake →Partner link: booking through this link supports the site at no extra cost to you.How late into autumn can you swim?
Guides give an average of 18 to 20°C in September and 14 °C in October. The reading of 12 September 2026 was above the September range, which happens after a hot summer: the lake holds its warmth longer than the air.
Mid-September is therefore a good time, with beaches almost empty. By late September, swimming becomes a matter of habit; in October, a matter of wetsuits. No source publishes a single end date for lifeguard cover across all the beaches.
How should you read a lake temperature before diving in?
Three questions are enough. Who measured it: an identified probe or a calculation? Where: in Annecy, in a southern bay, out on open water? When: this morning, yesterday, or a monthly average?
The tourist office reading answers all three. Most other pages answer only one. For the season and the averages, see the month-by-month page; for everything else about the lake, Lake Annecy in figures.
And for what the day costs once you are in the water, from lakeside parking to paid activities, parking in Annecy and things to do in Annecy give the prices we found.
If the probe shows less than 20°C, the lake is still open: paddleboarding, kayaking, sailing and cruises do not require getting wet. The Annecy activities page brings the trips together with their duration and price.
See activities on Lake Annecy →Partner link: booking through this link supports the site at no extra cost to you.Sources
Lake Annecy tourist office (weather page, SRV Annecy sailing club readings of 11 and 12 September 2026; English weather-forecast page), lacs.fr (Lake Annecy and Lake Annecy Talloires pages, 2026), annecy-meteo.com (2026), meteoannecy.fr (2026), eautemp.com and seatemperature.net (2026).
hautesavoiemontblanc-tourisme.com (lakes weather), cvsevrier.fr (sailing club weather), annecyvibes.com (2026), profilplongee.fr (2026). Research consolidated on 12 September 2026. The reading quoted on this page is driven by the facts table and is replaced without rewriting the article.
Frequently asked questions
What is the water temperature of Lake Annecy today?
Why don't websites give the same temperature for Lake Annecy?
Where is the temperature of Lake Annecy measured?
Can you still swim in Lake Annecy in September?
How cold is Lake Annecy at depth?
Camille Perrissin
Camille grew up in Sévrier, on the west shore, and swims in the lake from April to November. She has been taking the water temperature herself since 2019 and knows where the bottom suddenly drops away. She writes about the lake without ever turning it into a postcard.
