فَلَمَّا بَلَغَا مَجْمَعَ بَيْنِهِمَا نَسِيَا حُوتَهُمَا فَاتَّخَذَ سَبِيلَهُ فِي الْبَحْرِ سَرَبًا
[18:61]
So when they had reached the junction of the two (rivers) they forgot their fish, and it took its way into the sea, going away.
But when they reached the Junction, they forgot (about) their Fish, which took its course through the sea (straight) as in a tunnel.
And when they reached the point where the two met, they forgot their fish, and it took its way into the waters, being free.