Manuel Estiarte Duocastella (born October 26, 1961 in Manresa, Barcelona) is a former water polo player from Spain, considered by many the best of all time.

Estiarte has played 578 times for the Spanish team. With the national squad he won Olympic medals at Barcelona 1992 (silver) and Atlanta 1996 (gold). He won the World Championship at Perth 1998 after finishing in second place at Perth 1991 and Rome 1994. He is also the only one to have ever played in a record six Olympic games, the last of which was Sydney 2000. Estiarte was the top scorer in five of his six Olympics (the only exception being 1996, interestingly where he won his only gold medal with Spain)