The Blue Lagoon Was Never Supposed to Exist

Iceland's most photographed attraction started as industrial runoff. In 1976, the newly built Svartsengi Geothermal Power Plant began pumping its used geothermal seawater out into the surrounding lava field, the way plants like it always had. Except this particular water didn't drain away or evaporate — it pooled in the porous volcanic rock, turned a startling shade of milky blue, and never really left. Fifty years later, people fly in from across the world specifically to sit in it.

Born by Accident, Not Design

Nobody set out to build a spa. The Svartsengi plant exists to convert geothermal heat into electricity and hot water for the surrounding Reykjanes Peninsula, and the lagoon was simply where its by-product ended up — a literal industrial waste pool. It took a few years and one curious local before anyone realised what they had. In 1981, a resident named Valur Margeirsson began bathing in the runoff to see if it would help his psoriasis. It did, noticeably, and word travelled fast in a small country. By the mid-1980s, scientists had confirmed what bathers already suspected — the water was rich in silica, algae and minerals with real effects on skin — and in 1987, the first official bathing facility opened to the public.

Two Kilometres in the Making

The water itself has a genuinely dramatic origin story. It forms more than two kilometres underground, where fresh water and seawater meet under intense heat and pressure, reaching temperatures around a scorching 240°C before it's drawn up through geothermal wells. By the time it settles into the lagoon, it has cooled to a steady, bathing-friendly 38°C — warm enough to feel like a bath even with snow on the ground outside. The mix is roughly 70% seawater to 30% freshwater, and the whole lagoon is thought to renew itself entirely roughly every two days as fresh geothermal water cycles through.

Why It's Blue (and Sometimes Milky-White)

The colour comes down to one ingredient: silica. As the superheated water cools, silicon and oxygen from the surrounding lava solidify into fine white particles suspended in the water — the same silica that settles as soft white mud along the lagoon's edges, scooped up in buckets for guests to use as a face mask. Those particles scatter and reflect sunlight in a way that shifts the water's colour from milky-white to a vivid, otherworldly blue depending on the light and the angle you're looking from. Set against black volcanic rock and, depending on the season, a dusting of snow, the contrast is most of why photographs of the lagoon look almost implausible.

An Algae Found Nowhere Else on Earth

Silica isn't the only thing that makes this water unusual. A unique blue-green algae thrives in the lagoon's mineral-rich conditions and exists, as far as anyone has found, nowhere else on the planet — it was patented for skincare use in 2006. Between the silica, the algae and the mineral salts dissolved in the geothermal seawater, a dedicated clinic for chronic skin conditions opened on-site in 1995, and today the same three ingredients form the basis of the Blue Lagoon's own skincare line, sold in the lagoon's Mask Bar and well beyond it.

From Local Secret to World-Famous Spa

What opened as a single bathing facility in 1987 has grown into one of Iceland's biggest attractions, with steam rooms, saunas, a swim-up bar, in-water massage treatments and two on-site hotels — the Silica Hotel and the more exclusive Retreat Hotel, which has its own private lagoon access. Most visitors spend two to three hours in the water, and its location — at the foot of Mount Þorbjörn on the Reykjanes Peninsula, about 20 minutes from Keflavík International Airport — makes it a popular stop on the way in or out of the country, a way to soak away a long flight before it has even properly begun, or after one.

A power plant's runoff, turned by accident into the most photographed bath in the world.

Small Facts Worth Knowing

• The water starts at roughly 240°C— over two kilometres underground — before it's cooled to a bathing-friendly 38°C by the time it reaches you.
• It's a mix of seawater and freshwater — roughly 70/30 — meeting deep underground under extreme heat and pressure.
• The lagoon renews itself — the entire volume is estimated to cycle out and refill roughly every two days.
• Its algae exists nowhere else on earth — a blue-green species unique to this water, patented for skincare use in 2006.
• It sits at the foot of Mount Þorbjörn — on the Reykjanes Peninsula, about 20 minutes from Keflavík International Airport.
• It opened to the public in 1987 — nearly a decade after the runoff that created it first pooled in the surrounding lava field.

Before You Go

The lagoon operates year-round, and the water temperature barely shifts with the seasons, so a winter visit under the aurora is just as comfortable as a summer one under the midnight sun. In recent years, the lagoon has occasionally taken brief, precautionary closures during nearby volcanic activity on the Reykjanes Peninsula — standard practice for the area, and it has reopened each time once conditions were confirmed safe. Booking ahead is essential regardless of season, since daily visitor numbers are capped. And bring a hair tie: the geothermal minerals that are so good for skin are considerably less kind to hair left loose in the water.