Deildartunguhver (Icelandic pronunciation: [ˈteiltarˌtʰuŋkʏˌkʰvɛːr̥]) is a hot spring in Reykholtsdalur, Iceland. It is characterized by a very high flow rate for a hot spring (180 liters/second) and water emerges at 97 °C. It is the highest-flow hot spring in Europe.Some of the water is used for heating, being piped 34 kilometers to Borgarnes and 64 kilometers to Akranes.
A fern called Struthiopteris fallax, grows in Deildartunguhver. This fern is the only endemic fern in Iceland, and it does not grow anywhere else in the world.