Lake Þingvallavatn is Iceland’s largest natural lake and one of the country’s most important freshwater ecosystems. Located inside Þingvellir National Park, the lake plays a central role in Icelandic geology, history, and outdoor recreation. It is also closely connected to the famous Silfra fissure, where glacial meltwater flows from the lake through underground lava fields.
Where Is Lake Þingvallavatn Located?
Lake Þingvallavatn lies about 45–50 km (28–31 miles) east of Reykjavík, inside Þingvellir National Park. The drive usually takes 45–60 minutes, depending on weather and traffic. Most visitors reach the area via Route 36, which is fully paved and accessible year-round, though winter conditions may require caution.
Because the lake sits directly on the Golden Circle route, it is often visited together with Geysir and Gullfoss. Unlike those short stops, however, Þingvallavatn rewards visitors who spend more time exploring its shoreline, viewpoints, and walking paths.
Size, Depth, and Key Facts
Lake Þingvallavatn is the largest lake in Iceland, covering approximately 84 km² (32 sq miles). Its average depth is around 34 meters, with a maximum depth of about 114 meters, making it deeper than it appears from the shore.
The lake is fed by springs and groundwater filtered through porous volcanic rock. This natural filtration is why connected fissures like Silfra have exceptionally clear water, with underwater visibility often exceeding 100 meters.
Key facts at a glance:
- Surface area: ~84 km²
- Maximum depth: ~114 m
- Elevation: ~100 m above sea level
- Water type: Freshwater, spring-fed
- Protection status: Part of Þingvellir National Park (UNESCO World Heritage Site)
Geological Significance and Rift Valley Setting
Lake Þingvallavatn sits directly within the Mid-Atlantic Ridge, where the North American and Eurasian tectonic plates slowly pull apart. This rifting process shapes the lake’s basin and creates dramatic surface fissures such as Almannagjá and Hrafnagjá.
Over time, earthquakes and lava flows altered the lake’s size and depth. Compared to glacial lakes in northern Iceland, Þingvallavatn is primarily tectonic in origin, which makes it geologically rare even by Icelandic standards.
Water Quality and Ecosystem
The lake is known for its high water clarity and low nutrient levels. Because most inflow comes from underground springs rather than rivers, sediment levels are minimal. This creates stable conditions for aquatic life but also makes the ecosystem sensitive to disturbance.
Lake Þingvallavatn supports several fish species, including:
- Arctic char (multiple distinct populations)
- Brown trout
- Three-spined stickleback
Some Arctic char populations in the lake are considered scientifically important due to their unique adaptations. Fishing is regulated and requires permits, which helps protect these fragile populations.
How Lake Þingvallavatn Compares to Other Icelandic Lakes
Compared to Lake Mývatn, which is shallow and biologically rich, Þingvallavatn is deeper, clearer, and more geologically focused. Unlike Jökulsárlón, it is not glacial and has no floating icebergs. Its main value lies in its tectonic setting, water purity, and historical significance rather than dramatic surface features.
Is Lake Þingvallavatn Worth Visiting?
For travelers interested in Iceland’s geology, freshwater systems, and protected landscapes, Lake Þingvallavatn is one of the most meaningful stops in the country. It offers quiet depth rather than spectacle, and its importance becomes clearer the more time you spend understanding how it connects Iceland’s geology, ecology, and human history.
For those already visiting Þingvellir or Silfra, taking time to explore the lake itself adds essential context to the experience and helps explain why this area is protected at the highest level.