Lac de Guerledan, Brittany, France

Lake Locations:

France - Western France - Brittany -

Also known as:  Lake Guerledan

Lac de Guerledan is the largest lake in Western France’s Brittany tourism region, situated deep within the Argoat forest. The artificial lake is a family-friendly destination formed where the Blavet River meets the Nantes-Brest canal. This French waterway connects the municipalities of Brest and Nantes, and is navigable from Lake Guerledan. It stretches for an impressive 209 miles and features 158 locks.

The construction of Lac de Guerledan’s hydroelectric dam was begun in 1923 when engineers changed the flow of the Blavet River, but not completed until 1930 when the dam was finally put into service. The dam stands 155 feet high and 660 feet wide, and serves to provide hydroelectric power and flood control to surrounding regions. Every ten years the dam is drained for maintenance, and the city that used to exist beneath Lake Guerledan – formerly known as Ys – is revealed like magic.

Lac de Guerledan has a surface area of 988 acres and a normal elevation of 397 feet above sea level. With a maximum depth of 164 feet, it is known for both its aesthetic appeal and its wide array of water sports and recreational activities.

The irregular shores at Lac de Guerledan are perfect for carp fishing. Anglers reel in catches of pike, trout and perch populations at Guerledan Lake and its surrounding rivers. Zander, a species of fish that looks like a cross between pike and perch, is known to reach weights of up to 20 pounds here; most weigh between three to seven pounds.

Alternatively, visitors can spend a relaxing afternoon canoeing, kayaking and soaking up the sun along Lac de Guerledan’s sparkling beaches; adventurous types might try rock climbing one of the nearby gorges. For mountain biking enthusiasts, there are almost 300 trails in the area – but in France it is known as VTT, which stands for Velo Tout Terrain.

An on-site sailing school with water ski and pedal boat rentals makes for an exciting and educational afternoon at Lac de Guerledan. Canal boats known as ‘vedettes’ are also available to take visitors on peaceful sightseeing tours around the lake. Golfers should play a round at one of the local 18-hole championship courses, while trailblazers could spend an eternity hiking along the endless trails of the Argoat Forest. Horseback riding and ATV trails are also available for public use.

Several interesting towns and landmarks surround Lac de Guerledan. Head to Pontivy, Rostrenen and Quintin for a shopping fix, or to Mur de Bretagne’s Friday night evening market. During the summer, Breton hosts a number of dances and music festivals, the most famous of which is Fest Noz, or “Festival of the Night.” In Medieval times, this celebration was designed to encourage dancers to stomp their feet to firmly pack down a freshly-made floor. Fest Noz and St Gilles Vieux-Marche are held in July, and the Mur de Bretagne in August.

For a great day trip from Lac de Guerledan, check out the Armorique Regional Natural Park. Established in 1969, this reserve is the second oldest protected park in the history of France. It is composed of 425,000 acres and covers four distinct areas: the Iroise Sea islands, the Crozon Peninsula, the riverl Aulne, and the rocky Monts de’Arree. UNESCO calls the Molene archipelago, which is home to Europe’s largest seaweed field, “the reserve of the biosphere” for its rich wildlife and populations of seals and bottlenose dolphins.

Another nearby site of interest is the dolmen specimens at Liscuis, just a few minutes from Lac de Guerledan. These prehistoric tombs are composed of long, flat stones balanced on top of upright ones. The town of Saint-Aignan is home to a museum of electricity, which teaches about the history and science behind the Guerledan dam. If you are looking for a party, the best place to go for an upbeat nightlife scene is Pontivy. The largest city in the area, Pontivy, boasts an array of restaurants and pubs.

Real estate properties and vacation rentals are available around Lac de Guerledan, some on 19th century farms with homegrown fruit and vegetables. Come see Lac d’Guerledan for yourself to experience nature and make long-lasting memories.

Things to do at Lac de Guerledan

  • Vacation Rentals
  • Fishing
  • Boating
  • Sailing
  • Swimming
  • Beach
  • Canoeing
  • Kayaking
  • Water Skiing
  • Golf
  • Hiking
  • Rock Climbing
  • Biking
  • Horseback Riding
  • Wildlife Viewing
  • Museum
  • Shopping

Fish species found at Lac de Guerledan

  • Carp
  • Perch
  • Pike
  • Trout
  • Zander

Lac de Guerledan Photo Gallery

    Lac de Guerledan Statistics & Helpful Links

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    Lake Type: Artificial Reservoir, Dammed

    Water Level Control: EDF, Electricite de France

    Surface Area: 988 acres

    Normal Elevation (Full Pond): 397 feet

    Maximum Depth: 164 feet

    Water Volume: 44,589 acre-feet

    Completion Year: 1930

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    Trophic State | LakeLubbers

    Trophic State measures the level of algae and nutrients in a lake.

    An oligotrophic lake is very clear (blue in color) and does not support much plant or fish life. A hyper-oligotrophic lake is the clearest of all lakes, and is nearly devoid of plants and fish.

    A mesotrophic lake is slightly green and supports a moderate degree of plant and fish life. A lake's most desired trophic state is generally this mid-point - the mesotrophic state.

    A eutrophic lake is somewhat murky and supports a large amount of plant and fish life. A hypereutrophic lake is clouded with algae, plant life, and fish life. A eutrophic or hyper-eutrophic lake can be difficult to navigate by boat - and is often an unpleasant place to swim.

    The use of phosphorus-rich and nitrogen-rich fertilizer on lawns and golf courses surrounding a lake can cause it to become eutrophic or hypereutrophic.


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    Catchment or Drainage Area | LakeLubbers

    This is the surrounding area that drains into a lake, including land, rivers and their tributaries. This is also known as the lake's "catchment basin".

    Small lakes at the highest peaks of mountains have small drainage areas. The world's oceans have the largest drainage areas.


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    Lake-Area Population | LakeLubbers

    This is the estimated number of people who live in a house with a view of a lake, plus those who self-describe the lake as their home, for example: "I live at Smith Mountain Lake."


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    Water Residence Time | LakeLubbers

    This is the estimated time that it takes for an amount of water equal to the entire volume of a lake to flow out of - or evaporate from - the lake.

    Residence Time can be as short as a few days for fast-flowing small lakes, and can exceed 100 years for slow-flowing large lakes.


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    Completion Year | LakeLubbers

    This is the year that a reservoir was first filled to the reservoir's normal elevation - or the year that a natural lake was first dammed. A large reservoir can take more than a year to fill after its dam is first closed.

    The Grand Anicut in southern India is generally considered the world's oldest dam that still operates. Grand Anicut was constructed in the second century BC. It now impounds an irrigation network that includes roughly one million acres.

    You can find many of the the world's newest reservoirs on LakeLubbers. Many of the world's oldest reservoirs appear on the last page of that list.


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    Water Volume | LakeLubbers

    This is the estimated volume of water that a lake contains -- measured at the lake's normal elevation. By this measure, the world's largest freshwater lake is Siberia's Lake Baikal.

    You can find many of the the world's largest lakes (by water volume) on LakeLubbers.

    Water Volume can be measured in acre-feet, in cubic miles, or in cubic kilometers. One acre-foot is the amount of water needed to cover one acre (43,560 square feet) to a depth of one foot. One cubic mile equals 3,379,200 acre-feet. One cubic kilometer equals 810,713 acre-feet.

    1 acre-foot is equal to 325,851 US gallons. Siberia's Lake Baikal contains about 6,276,367,740,000,000 gallons of freshwater - nearly 1 million gallons for every living person on earth.

    The other - and more widely used - measure of a lake's size is the lake's surface acreage. By that measure, the world's largest freshwater lake is North America's Lake Superior.


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    Maximum Depth | LakeLubbers

    This is the estimated greatest depth of the water in a lake -- measured at the lake's normal elevation. The world's deepest lake is Siberia's Lake Baikal; that lake's maximum depth is estimated at 5,314 feet.

    You can find many of the the world's deepest lakes on LakeLubbers. If you select the last page of that list, you will find the (maximum depth of) the shallowest lakes in our database.


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    Average Depth | LakeLubbers

    This is the estimated average depth of the water in a lake -- measured at the lake's normal elevation. If the water volume and surface area of a lake are known, an estimate of the lake's average depth can be calculated:

    Water volume ÷ Surface Area = Average Depth

    Example: 1,000,000 acre-feet ÷ 20,000 acres = 50 feet average depth


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    Maximum Elevation | LakeLubbers

    This is a lake's highest water level, measured by the lake's surface distance above sea level, that can occur during flooding. A lake's highest possible maximum elevation is usually the top of the lake's dam or spillway.

    At lakes that include residential development, government regulations usually forbid the construction of homes below a lake's maximum elevation.


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    Minimum Elevation | LakeLubbers

    This is a lake's lowest water level, measured by the lake's surface distance above sea level, that can be reasonably expected to occur. Low lake levels can occur due to deliberate seasonal draw downs for irrigation or impending snow melt, reduced water inflows, drought and evaporation, residential or commercial water demands, and hydropower generation.

    Some lakes' minimum and maximum elevations are virtually the same. Lakes that generate hydropower may vary by several feet - according to power demand. Lakes whose primary purpose is to prevent flooding can seasonally vary by 100 feet or more.

    When some lakes reach their minimum elevation, their boat ramps may not be long enough to permit boat access - and boats docked on shallow parts of the lake may end up on dry ground. In those cases, kayakers and shore-based anglers may be among the few happy recreational users of the lake.


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    Normal Elevation | LakeLubbers

    This is a lake's normal water level, measured by the lake's surface distance above sea level. For a reservoir, this water level is also known as "full pond" or "full pool".

    You can find many of the world's highest-elevated lakes on LakeLubbers. Lakes with the lowest elevations (known by LakeLubbers) are shown on the final page of that list.


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    Shoreline Length | LakeLubbers

    This is the length of the exterior shoreline around a lake - measured at the lake's normal elevation. The shoreline length can be considerably shorter or longer when lake water levels are lower or higher than normal.

    A lake with many coves has a much longer shoreline than a lake of similar surface area that is nearly circular in shape.

    When known, the shoreline miles that we report in our statistics include only the lake's exterior shoreline, and exclude the shorelines of islands located within a lake's boundaries. In lakes with many islands, those islands' combined shorelines may exceed a lake's exterior shoreline.

    You can find many of the world's longest-shoreline lakes on Lakelubbers.


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    Surface Area | LakeLubbers

    This is the area (acreage, square kilometers, etc.) of the top surface area of a lake - measured at a lake's normal elevation. The surface area can be considerably smaller or larger when lake levels are lower or higher than normal. North America's Lake Superior is the world's largest freshwater lake by this measure.

    The other measure of a lake's size is the lake's water volume. By that measure, the world's largest freshwater lake is Lake Baikal in Siberia.

    You can find many of the world's largest lakes (acres) on Lakelubbers. There is no widely-accepted minimum surface area that defines a lake. What Lakelubbers describes as a lake, you might call a pond. The smallest lake that Lakelubbers currently includes is Hawaii's 2-acre Lake Waiau.


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    Water Level Control | LakeLubbers

    This is the organization that controls water releases or outflows from the lake or reservoir. In the USA, this is often the US Army Corps of Engineers, a power company, a municipal water system, an irrigation district, or a paper manufacturing company. In the case of private or gated lakes, a homeowners' association may be the lake's controlling authority.

    Many lakes cross borders, including North America's Great Lakes. The control of such lakes and their coveted freshwater may be amicably shared - or hotly disputed.

    "Water wars" continue at many lakes as growing populations and crop irrigation needs compete for the freshwater that lakes contain.


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    Lake Type | LakeLubbers

    There are 3 basic types of lakes that are currently included on LakeLubbers. 2 types may be dammed or not dammed, producing 5 classifications.

    - A Reservoir is a man-made freshwater lake that is usually created by damming rivers.

    - A Natural Freshwater Lake occurs naturally - often by glacial activity - and has a salinity of less than 30 parts per thousand. It may be dammed to produce electricity or for other reasons.

    - A Natural Saltwater Lake occurs naturally and has a salinity of more than 30 parts per thousand (ppt). It may be dammed.

    "Brackish" water may be categorized as freshwater or saltwater, depending on its salt content (salinity). Oligohaline water has less than 15 ppt of salt. Mesohaline water has 15-29 ppt. Polyhaline has 30-335 ppt.


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