In Hydrocution death occurs by

Immersion Syndrome (Hydrocution): Death in immersion syndrome is due to cardiac arrest as a result of vagal inhibition. It is produced by (i) Cold water stimulatung the nerve endings of the surface of the body (!!) Cold water striking the epigastrium and (!!!) Cold water entering the ear drums, mucosa of pharynx or Larynx. Alcohol increases such effects due to general vasodilatation. Reff: The synopsis of forensic medicine&Toxicology 28th edition pg:191