Complex sentence: The Icelandic records in swimming are the fastest ever performances of swimmers from Iceland, which are recognised and ratified by the Icelandic Swimming Association (Sundsamband Íslands-SSÍ).
Split into simpler sentences: The Icelandic records in swimming are the fastest-ever performances by an Iceland swimmer. The records are recognised and ratified by the Icelandic Swimming Association ("Sundsamband Íslands"-SSÍ).