According to the Brazilian media, Cesar Cielo, Olympic champion and world champion in the 50 and 100m freestyle, tested positive for furosemide; ( a diuretic and a masking agent), this past May. The Brazilian Swimming Federation gave him a only a warning but may conduct an investigation.
From Sport 24:
Tested positive in May" "...World champion of 50 and 100m freestyle in 2009 in Rome and a favorite in both distances at the end of the month at the World Shanghai has indeed been a positive drug test with furosemide, a diuretic banned because it allows in particular to mask making other products. Control took place at the Maria Lenk Trophy in May in Brazil. Three other swimmers (Nicholas Santos, Henrique Barbosa, Vinicius Waked) also tested positive for the same product. A monitoring committee, set up by the Brazilian Confederation of water sports, Cesar Cielo and auditioned three swimmers complained of having to explain what their positive control.