The disciples see Jesus walking on the sea and become afraid. He answers, 'Ego eimi; be not afraid.' In ordinary Greek the expression can naturally mean 'It is I,' identifying the speaker.
Within John's Gospel, however, the same words also participate in a larger pattern of 'I am' language.
Israel's Scriptures repeatedly portray mastery over the sea as belonging to God, including texts describing God treading upon the waves. John's account does not explicitly quote one such passage here, so individual Old Testament allusions should not be made more precise than the text permits. The Greek ego eimi is likewise ordinary self-identification in some contexts while carrying unmistakably stronger force in others, especially John 8:58.
John then says the boat immediately reaches its destination after the disciples receive Jesus.
The linguistic caution allows both levels of the scene to remain intact. Jesus truly tells frightened disciples, 'It is I,' but the evangelist has placed that self-identification in an extraordinary display of authority over the sea.
For readers of the whole Gospel, the episode contributes to John's cumulative revelation of Jesus without requiring every use of ego eimi to function identically.