"Agua Mala" is Spanish for bad water and in some Latin American countries is slang for "Portuguese Man-of-War", otherwise known as a blue bottle (Physalia Physalis), a marine hydrozan.
Special make-up supervisor John Vulich considered the monster with its translucent tentacles as the hardest thing he had to do all season.
Gillian Anderson later joked that they got so wet in this episode, it was like being back in Vancouver.
This was Darren McGavin's final television acting role before his death on February 25, 2006 at the age of 83.
Six pairs of costumes were required for each cast member to replace all the wet clothing.