Ottův pramen, Mineral spring in Kyselka, Karlovy Vary Region, Czech Republic

Ottův pramen is a mineral spring in Kyselka whose water is piped from the Ottova kolonáda pavilion above the Ohře River to a drinking fountain placed before the statue of Heinrich Mattoni, between Jindřichův dvůr and the café. Until 2014 the fountain stood at the corner of the Jindřichův dvůr building. The water then runs in a channel down to the Ohře.

Commercial water production began in 1867 when Heinrich Mattoni started bottling mineral water from the source. This venture established the area as an important center for mineral water extraction and trade.

The spring was renamed König-Otto-Quelle on 23 August 1852 after the Greek king Otto I, who had visited Kyselka that year; before that it was called Buchsäuerling or Bukovská kyselka after the Buchberg above the village. The name was dropped in 2013, when the neglected Mattoni-Quelle was renamed Otto-Quelle again.

The spring is tapped at a drinking fountain in front of the Heinrich Mattoni statue, between Jindřichův dvůr and the café; until 2014 the fountain stood on the corner of the Jindřichův dvůr building. The water is also piped to the Karlovarské minerální vody bottling plant. The natural outlet on the south side of the former spa, near the Villa Mattoni park, has never been precisely located.

The spring was renamed Mattoni-Quelle after 1945 and only regained the name Otto-Quelle in 2013; it was declared a monument in 2010. Its exact natural outlet could not be determined despite soil surveys between 1959 and 1966 and again in the 1980s.