Lake Þingvallavatn

Þingvallavatn is Iceland's largest natural lake, filling the rift valley directly south of Þingvellir National Park on the first leg of the Golden Circle. The old parliament site of Þingvellir sits on its northern shore, so anyone who stops at the Almannagjá gorge or the Hakið viewpoint is already looking straight down the lake. At about 84 km², Lake Þingvallavatn stretches so far south that its only outflow, the Sog river by Úlfljótsvatn, is out of sight from the park.

Most visitors see it from the north shore and keep moving. That is a pity, because the lake is the reason Þingvellir looks the way it does, and it repays an hour of slower driving along the shore roads.

Where is Þingvallavatn?

Þingvallavatn lies in the same rift valley as Þingvellir, between Botnssúlur in the west and Lyngdalsheiði in the east, with the Hengill volcano rising at its southern end. The lake sits about 100 metres above sea level. Route 36 (Þingvallavegur) reaches the north shore from Reykjavík over Mosfellsheiði, passes through the national park, then runs down the eastern side of the lake towards the Sog.

The western shore has its own road. Route 360 (Grafningsvegur efri) leaves Route 36 west of the lake and winds south past Nesjavellir to Úlfljótsvatn, a paved road that sees a fraction of the Golden Circle traffic.

Why Þingvallavatn is special

Almost none of the water in Þingvallavatn arrives by river. According to the national park's watershed figures, around 90% of the inflow comes through underground channels. The catchment covers about 1,300 km² and is mostly porous lava.

Rain falling on that lava reaches the lake in two to four months. Meltwater from Langjökull, about 50 km to the north, takes 20 to 30 years.

That long journey through rock filters the water and loads it with minerals. It is why Silfra, a spring-fed fissure on the northern shore, is clear enough for snorkellers to see the fissure walls far below, and why the lake supports far more life than its cold temperature suggests.

How deep is Þingvallavatn?

The deepest point is 114 metres, which takes the lake bed below sea level, given that the surface sits only about 100 metres up. The lake lies in a valley that is still pulling apart. Movement of the North American and Eurasian plates has opened fissures along the shore and dropped the valley floor over thousands of years, and you can see the result in the cracks that run straight into the water around Þingvellir.

Islands and the Sog river

Several islands rise from the lake, and their volcanic origin is easy to see from the shore. The lake has only one outflow, the Sog, which leaves at the southern end near Úlfljótsvatn and flows south to join the Hvítá. After the last Ice Age, eruptions at Skjaldbreiður and Eldborgir blocked the old glacial river from the north and partly dammed the Sog, which is how the lake's fish came to be trapped here.

Fish in Þingvallavatn

Þingvallavatn holds three of Iceland's five freshwater fish species: brown trout, Arctic char and the three-spined stickleback. The char are the reason biologists come here. Over roughly 10,000 years they have split into four distinct forms that feed and breed in different parts of the lake, from a large fish-eating char to a dwarf form.

The brown trout are famous among anglers because they grow large. The park warns that trout over 60 cm may contain high levels of mercury and advises against eating them, particularly for pregnant and breastfeeding women.

Smaller life is just as striking. Up to 120,000 small animals per square metre live on the stony shore, and tiny groundwater amphipods found in the lake are thought to have survived the Ice Age in water warmed by geothermal heat beneath the ice sheet.

Fishing in Þingvallavatn

You can fish the northern shore inside the national park, from Leirutá at Lambhagi round to Langitangi south of Arnarfell. The park's angling rules set the season from 20 April to 15 September and the day permit at ISK 2,500 per rod, sold at the service centre at Leirar and online. Holders of the Veiðikortið fishing card can also fish here, and children fish free with an adult who holds a permit.

The rules are strict, and rangers check them:

• 20 April to 31 May: fly fishing only, and every brown trout must be released
• 1 June to 15 September: fly, worm or lure allowed; no other bait
• Shore or small near-shore islets only; no boats, float tubes or nets
• Ólafsdráttur is closed from 1 July to 1 September for char spawning
• No fishing in the Öxará river or south of its mouth

Every catch has to be logged online with the Marine and Freshwater Research Institute, kept or not. Vatnskot is the most popular spot, with a wooden pier, toilets and a tents-only campsite in summer. Used fishing gear brought from abroad must be disinfected before use, and the service centre can do it for ISK 5,000.

Things to do at Þingvallavatn

For most visitors, the lake is part of a Þingvellir visit rather than a separate trip. Our Golden Circle horse tour stops at Þingvellir on the lake's north shore, where the view down the water opens up, though it does not drive the quieter shore roads.

See the lake from Hakið and Almannagjá

The best overview is from the Hakið viewpoint at the top of Almannagjá, next to the visitor centre, where the whole lake opens out to the south with the islands and Hengill behind. Walk down through the gorge towards Þingvellir church and the shore, and you see how the fissures run straight into the water.

Snorkel or dive in the lake's springs

Diving is allowed in two fissures in the park. Silfra is the famous one (see our guide to Silfra fissure for how snorkelling there works), while Davíðsgjá lies in the north-eastern part of the lake itself and is reached by swimming out from the shore. The water in both is 2 to 4 °C, so divers must wear drysuits and snorkellers need a drysuit or a thick wetsuit.

Drive the shore roads

If you have a car, take Route 360 along the western shore instead of driving straight back to Reykjavík. The road climbs over low ridges with views across the water to the islands, passes the steam of Nesjavellir under Hengill, and comes out at the southern end of the lake. From there you can continue past Úlfljótsvatn at the southern end to the Sog and rejoin Route 36.

Boats cannot be launched from the national park shoreline, so kayaking and boating are not activities you can do here independently.

How to get to Þingvallavatn

From Reykjavík, take Route 1 north to Mosfellsbær and turn onto Route 36, which crosses Mosfellsheiði to Þingvellir and the north shore. The P1 car park at Hakið is the usual first stop, and P5 at Valhöll is closest to the shore, Silfra and the church.

A national park parking fee of 1,000 ISK for a car with up to five seats covers P1, P2 and P5 for the whole day. We explain how payment works in our guide to Þingvellir parking charges. The fee applies only at those three car parks, so the lay-bys along Route 360 on the western shore cost nothing.

Best time to visit Þingvallavatn

The lake is open to view in every month. From June to August, summer brings long daylight, the full angling season and the best conditions for the shore roads. September is quieter and often calm, with birch woods on the slopes turning colour.

In winter the low sun lights the lake from the south, but the wind across the open water is bitter. Route 36 through the park is the main Golden Circle road, while Route 360 is a minor one, so check umferdin.is before driving it in snow.

How long to spend at Þingvallavatn

Twenty minutes at the Hakið viewpoint gives you the classic view, and most Golden Circle visitors spend an hour or two at Þingvellir in total. Add about an hour if you want to drive Route 360 along the western shore and stop at a few lay-bys. Anglers, of course, can lose a whole day here.

Photo: Diego Delso, CC BY-SA 4.0, via Wikimedia Commons