योऽप्सु तिष्ठन्नद्भ्योऽन्तरो यमापो नविदुर्यस्यापः शरीरं योऽपोऽन्तरो यमय-त्येष त आत्मान्तर्याम्यमृतः ॥ ४ ॥
In plain words
The one who lives within the waters, yet is other than the waters, whom the waters themselves do not know, whose body the waters are, who governs the waters from inside -- he is your self, the one who rules from within, and he does not die.
Close to the Sanskrit
He who, dwelling in the waters, is other than the waters, whom the waters do not know, whose body is the waters, who controls the waters from within -- he is your self, the inner controller, immortal.