Llyn Clywedog, Wales, United Kingdom

Lake Locations:

United Kingdom - Wales - Mid Wales -

Also known as:  Lake Clywedog, Clywedog Reservoir

The Clywedog Reservoir, or Llyn (Lake) Clywedog, was formed by damming the River Clywedog, a tributary of the River Severn, in 1967. The concrete buttress dam is the tallest concrete dam in the United Kingdom, with a height of 236 feet (72 meters) and a length of 755 feet (230 meters). The reservoir is located in Mid-Wales near the town of Llanidloes in Powys. The location for the reservoir was chosen to take advantage of high rainfall in the Welsh hills. This rainfall is stored and released from Llyn Clywedog in times of high demand, particularly during extended dry periods. In addition to supplying the Clywedog Valley with sparkling clean water, the reservoir also provides a recreation destination for scenic walks, excellent fishing, and wildlife watching.

At 615 acres (2.5 square kilometers) Llyn Clywedog is considered one of the most beautiful lakes in Wales, offering stunning scenery and a perfect habitat for wildlife. Red kites (a species of bird once nearly extinct), buzzards, Canada geese, peregrine falcons, and ospreys are common sights. Squirrels, polecats, foxes, and the short-tailed vole inhabit the lake’s shoreline.

Llyn Clywedog is owned and operated by Severn Trent Water Limited which has constructed a number of walking trails around the lake. Visitors can also drive around the reservoir and stop at a number of picnic and scenic observation points for a wonderful view of the lake and the stunning area. A viewing area located above the dam called the Look Out offers an elevated covered platform where guests of the lake can enjoy a spectacular panoramic view, and (weather permitting) a welcoming cup of tea and a snack. The National Trail of Glyndwr’s Way passes beneath the dam before following a course along the southern shore of the lake.

For cyclists, there are various trails in the area including a route which begins in the town of Llanidloes, passes through the Hafren Forest, around Llyn Clywedog and returns to Llanidloes. The round trip id approximately 19 miles (30.5 kilometers).

Llyn Clywedog is amply stocked with brown trout and rainbow trout by the Llanidloes Angling Society. The season for both rainbows and browns begins on March 18th. The brown trout season finishes on October 7th with the rainbow season closing on November 30th. Fly fishing is the only form of fishing allowed on the lake. Fishing competitions, such as the European Bank Competition, are held regularly on Lake Clywedog.

Sailing on Llyn Clywedog is managed by the Clywedog Sailing Club. The organization holds numerous competitions and regattas throughout the year where visitors are always welcome. Measuring just under six miles (9.5 kilometers) long, the lake is open to all types of non-powered watercraft. Boats for fishing, canoeing, and sailing are available for rent.

Vacation rentals and holiday accommodations can be found in the ancient market town of Llanidloes, just south east of Llyn Clywedog. Llanidloes offers hotels, charming bed & breakfasts, holiday cottages, and a number of self-catering options. Camping and caravan parks can also be found within a short drive from the town. Llanidloes is the first town on the River Severn and an ideal base spot for exploring the Mid-Wales area. The town also offers a golf course, shopping, an equestrian center, and miles of trails for walking, hiking and biking. The Hafren Forest lies just northwest of Llanidloes and covers 9,884 acres (40 square kilometers) of mainly pine and spruce trees for hiking, mountain biking and horseback riding.

For an interesting daytrip, the Brecon Beacons National Park is an easy drive south of Llyn Clywedog and contains the highest mountain peaks in South Wales. The National Park stretches from Llandeilo in the west to Hay-on-Wye in the northeast, covering 520 square miles (1,344 square kilometers) of mountains, rolling countryside, woodland, waterfalls, and caves.

West of Llyn Clywedog on the Cardigan Bay sits the seaside town of Aberystwyth. Home to Aberystwyth University, this beautiful community boasts a number of attractions including a wide selection of specialty clothes shops, a historic narrow gauge cliff railway, two wonderful sandy beaches, the remains of a Welsh castle, and a huge choice of pubs, cafes, restaurants, holiday cottages and all sorts of vacation rentals and real estate.

With fantastic fishing and endless trails for hiking, outdoor enthusiasts will find the sparkling waters of Llyn Clywedog a great base for exploring the surrounding hills, valleys, and lush forests. Featuring some of the region’s most scenic and isolated countryside, the wild beauty of the area makes it one of Wales’ most exhilarating places to visit.

Things to do at Llyn Clywedog

  • Vacation Rentals
  • Fishing
  • Boating
  • Sailing
  • Swimming
  • Beach
  • Canoeing
  • Golf
  • Camping
  • Picnicking
  • Hiking
  • Biking
  • Horseback Riding
  • Waterfall
  • Wildlife Viewing
  • National Park
  • Shopping

Fish species found at Llyn Clywedog

  • Brown Trout
  • Rainbow Trout
  • Trout

Llyn Clywedog Photo Gallery

Llyn Clywedog Statistics & Helpful Links

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Lake Type: Artificial Reservoir, Dammed

Water Level Control: Severn Trent Water Limited

Surface Area: 618 acres

Normal Elevation (Full Pond): 880 feet

Maximum Depth: 217 feet

Water Volume: 40,536 acre-feet

Completion Year: 1967

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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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