submersion
From Longman Dictionary of Contemporary Englishsubmersionsub‧mer‧sion /səbˈmɜːʃən $ -ˈmɜːrʒən/ noun [uncountable] UNDER/BELOWthe action of going under water, or the state of being completely covered in liquidExamples from the Corpussubmersion• I had imagined that friendship meant giving up privacy, and closeness meant complete submersion in the other person.• During submersion, the paper fibres become thoroughly saturated with sizing.• In contrast, dolphins dive with only the gas in their system at the time of submersion.