Joachim O. Fernandez (August 14, 1896-August 8, 1978) was a member of the U. S. House of Representatives representing the state of Louisiana. He was a Democrat.
Fernandez was born in New Orleans. He began his political career as a member of the Old Regular political machine and was a state senator under New Orleans mayor T. Semmes Walmsley. In 1930 he defected to the camp of Walmsley's enemy, governor Huey Long. He became Long's Ninth Ward political boss, and was elected to the House of Representatives in 1933 with Long's support. He lost his seat in 1940 to reform candidate Felix Edward Hebert.
He served in the Second World War as a lieutenant commander in the United States Navy, and was the collector of internal revenue for New Orleans from 1943 to 1946. In the election of 1946, Fernandez briefly served as the reform candidate against New Orleans mayor Robert Maestri, but he withdrew from the race at the last minute after being bought off by Maestri's offer to pay his campaign expenses.
Fernandez was known as "Bathtub Joe" Fernandez for his habit of avoiding calls from reporters by claiming he was in the bath.