But when they reached the junction between the two [seas], they forgot all about their fish, and it took its way into the sea and disappeared from sight.

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.

So when they reached the junction of the two (rivers), they forgot their fish, and it took its way into the river, being free.

But when they reached the junction between them, they forgot their fish, and it took its course into the sea, slipping away.