There are two established professional marathon swimming circuits in the world, both sanctioned by FINA and organized by local race committees.
The FINA 10KM Marathon Swimming World Cup circuit are races limited to 10 kilometers held in oceans, seas, bay and lakes from Canada to China.
The FINA Open Water Swimming Grand Prix are longer races, ranging for 15 – 57 kilometers, held in seas, bays, lakes and rivers from Argentina to Dubai.
In 2009, a total of 264 athletes from 39 countries took part in the FINA 10KM Marathon Swimming World Cup circuit. France (67), Brazil (17), Russia (17) and the USA (15) had the most number of athletes participating on this circuit.
A total of 106 athletes from 25 countries took part in the longer FINA Open Water Swimming Grand Prix circuit with Argentina (20), Italy (13) and Germany (9) having the most number of athletes participating.
Photo shows Angela Maurer, gold medalist in the 25K race at the 2009 World Swimming Championships and nominee for the 2009 World Open Water Swimming Woman of the Year.