Surströmming (pronounced [ˈsʉ̂ːˌʂʈrœmːɪŋ]; Swedish for ''sour herring'') is a lightly-salted fermented Baltic Sea herring traditional to Swedish cuisine since at least the 16th century. The Baltic herring, known as strömming in Swedish, is smaller than the Atlantic herring, found in the North Sea. Traditionally, the definition of strömming is "herring fished in the brackish waters of the Baltic north of the Kalmar Strait". The herring used for surströmming are caught just prior to spawning in April and May.