Prestagilsfoss is a hidden multi-tiered waterfall in Prestagil at the head of Mjóifjörður in East Iceland. The narrow gorge cuts into the steep southern side of the fjord, close to the better-known Klifbrekkufossar waterfalls.
Although Prestagilsfoss may not appear particularly large when viewed from across the valley, the complete waterfall system is considerably more substantial. Prestagilsá descends through the deep gorge in at least five main drops. The total vertical descent has been estimated at around 160 metres, with the largest individual drop estimated at approximately 60 metres or more. These figures are estimates rather than precise surveyed measurements.
The three lower sections of the waterfall can be seen relatively clearly from across the valley, while the upper drops are partly hidden by the narrow shape of the gorge. As a result, only part of the complete waterfall system is visible from any single viewpoint.
Prestagil is also associated with an old local folktale that explains its unusual name, meaning "the Priests' Gorge". According to the story, a giantess lived in the gorge and lured priests from Mjóifjörður into her home. An old version of the tale names the two priests as Snjólfur and Tómás and says they disappeared on separate Christmas nights.
Prestagil lies near the head of Mjóifjörður, close to Klifbrekkufossar. The surrounding landscape is characterised by steep mountainsides, narrow ravines and numerous waterfalls cascading towards the fjord.
Mjóifjörður is one of the more remote fjords of East Iceland. The road into the fjord is seasonal and access can be limited outside summer. Prestagil itself is not a developed visitor attraction, so visitors approaching the gorge should take particular care.