Jökulsá (Icelandic pronunciation: [ˈjœːkʏlsˌauː auː ˈpreiːðaˌmɛr̥kʏrˌsantɪ]) is a river in Southeast Iceland in Austur-Skaftafellssýsla (municipality) in the middle of Breiðamerkursandur, a glacial outwash plain.

It connects the Jökulsárlón glacier lake with the sea, the Atlantic Ocean. The river is very short, at the moment about 500 m. It was still 1,500 m long in 1989, but its length was 1,000 m around the year 1900, when it discharged directly from the Breiðamerkurjökull glacier; the lake did not start to form until 1935–40. The lake grew very fast from 1950 onwards, and changed the course of the river. The medium discharge today is 250–300 m³/s. From time to time, icebergs from the lake enter the river.

Erosion could with time break down the spits and connect the glacier lake directly with the sea, forming a fjord. The government fights the erosion by stabilising the shoreline of the sea and also of the river, not least in order to save the road.

The Hringvegur (national ring road, route 1) crosses the river on a bridge. The rapid erosion by the sea is threatening the road. If the road were destroyed, East Iceland would be cut off from Reykjavík except by ferry or by a much longer northern route.

The bridge is built from concrete and is around 90 m long. It dates from 1967. Before that, the river crossing was very dangerous. Many people preferred to cross the glacier tongue instead. There was a boat ferry from 1932.

64°02′33″N 16°10′45″W / 64.0424°N 16.1792°W / 64.0424; -16.1792