In 2000 he swam the Danube River (2860 km) and had achieved the world's long distance swimming record (3004 km) in 58 days. In July 2001 he achieved one more world record - 504 km of non-stop swimming in Danube within 84 hours and 10 minutes. In 2002, he swam the entire Mississippi River (3885 km) in 66+2 days.
His first two rivers to beat were: in 1992 the river Krka (105 km) in his homeland, in 28 hours, and in 1993 the boundary river Kolpa (Croatian Kupa) (62 km), in 16 hours.
During his swims, he sleeps for 5 hours each day. He prepares himself for a such long swimming over a year and a half. It usually takes 6 to 7 months for Strel to recover his body in a normal state. The Nile has been proposed as his next place to swim, but he has said that no one can do such a thing.