He has merged the two seas that meet

Imam Ahmed Alhasan احمد الحسن a.s said

The objective of Moses pbuh was the junction of the two seas.
And Moses pbuh walks and reaches the junction of the two seas, yet he does not notice that he arrived, and so he bypasses him and then returns to him.
The fact that the objective of Moses pbuh is the junction of the two seas and the fact that he missed this objective needs pondering because you do not miss, for example, the junction of the Tigris and Euphrates if you track one of them downwards, so how did Moses and Joshua bin Noon pbut miss the junction of the two seas if it was just a location and a junction of two rivers? And how did they overlook the fact that they reached the junction of the two seas even though both of them are infallible?

Therefore, it must be that what Moses pbuh was seeking from the junction of the two seas is something that can be missed, and it is not just a junction of two rivers. Rather it must be that he who overlooks it does not earn the description of being weak in terms of his perception or foolish. And the truth is that the very least to be said about a person who overlooks and bypasses a certain junction of two rivers which he was seeking, is that he is weak in terms of his perception.

Therefore, the junction of the two seas cannot be a certain location, otherwise the overlooking by Moses pbuh of the junction of the two seas would discredit his perception as well as his infallibility. And it must be that observing, remembering, and initially knowing the junction of the two seas requires a high degree of sincerity, and infallibility (which is a result of this sincerity), higher than Moses’ pbuh degree of sincerity, and his infallibility (which is a result of his sincerity). This is in order for the oversight by Moses pbuh and Joshua pbuh of this matter, which Allah has charged Moses pbuh to reach, not be in opposition with their infallibility pbut.

Rather, in the saying of Moses,
﴾“I reach the junction of the two seas or I spend years and years in search of it.”﴿,
he pbuh has clarified from the beginning that the junction of the two seas is something which can be missed and that it requires a high degree of sincerity to know it. Therefore it must be that what Moses pbuh was seeking from the junction of the two seas was not the location, but rather it was the Virtuous Servant, and it was the first test of Moses pbuh to reach and know him. And although Moses pbuh did not succeed in reaching the Virtuous Servant and initially knowing him, he also did not entirely fail in reaching the Virtuous Servant. Rather, he reached him in the end, and this was the first lesson which Moses pbuh was taught in this journey.

And to further clarify what Moses pbuh was seeking from the junction of the two seas in this place from the Holy Quran, we must go back to another place in the Quran which mentioned the two seas and their junction but in another way which might be more clear and obvious to the one who ponders. This place is in the beginning of Surat Al-Rahman,
He swt said,
19. ﴾He has merged the two seas that meet.
20. There is a barrier between them. They do not encroach.
21. Which of the signs of your Lord will you both deny?
22. Pearls and coral come out from both of them.
23. Which of the signs of your Lord will you both deny?
24. And to Him belong the ships elevated in the sea like flags.
25. Which of the signs of your Lord will you both deny?
26. Everyone that is thereon will disappear,
27. and the Face of your Lord remains, Owner of Majesty and Favor.﴿
—Surat Al-Rahman (The Merciful) 55.

I do not want to explain and interpret these verses as the narrations that came from them [Ahlul Bayt] pbut explaining and interpreting them are sufficient to clarify them and their meaning clearly. But I only direct whoever wants to ponder them, in order to know what is intended from and within them, to read the saying of the Almighty
26. ﴾Everyone that is thereon will disappear
27. And the Face of your Lord remains, Owner of Majesty and Favor﴿

so that it would be clarified for him that everything before these two verses is an elaboration of the Face of Allah and a mentioning of the remaining Face of Allah by the attribute suitable for being the remaining Face of Allah, which is knowledge. And I do not believe that it is a hidden matter that water and sea in the Kingdom of Heavens are knowledge. I also do not believe that the remaining of the knowledge of the knowledgeable ones in this life even after they leave is a hidden matter, rather it remains even after the disappearance of this life, and this is what this verse came to clarify and confirm and introduce to people,
26. ﴾Everyone that is thereon will disappear
27. And the Face of your Lord remains, Owner of Majesty and Favor﴿

This face which Allah has faced the creation with, which is knowledge and the full intellect. And it is the water and the two seas, and it is what comes from them and what flows within them, and it is Muhammad and the progeny of Muhammad pbut, and the prophets and successors pbut, and the supporters of Allah swt.

As for the narrations which have clarified that the two seas are Ali and Fatima, and that whatever comes from them or flows within them are the Imams and the Mahdis pbut, they are many such as:
• From Abu Abdullah pbuh in what Allah pbuh has said:
﴾He has merged the two seas that meet ۝ There is a barrier between them. They do not encroach﴿, he said, “Ali and Fatima are two deep seas, not one of them encroach upon the other,” ﴾Pearls and coral come out from both of them﴿, he said, “Al-Hassan and Al-Hussein pbut.” Tafseer Al-Qummi Vol. 2 page 244
• From Ali bin Ibrahim in what He swt said, ﴾He has merged the two seas that meet﴿ he said, They are the Prince of Believers and Fatima pbut, ﴾Pearls and coral come out from both of them.﴿, Al-Hassan and Al-Hussein pbut. And what He swt said, ﴾And to Him belong the ships elevated in the sea like flags.﴿, this is what Al-Khansa said bewailing her brother, Sakhr. [Tafseer Al-Qummi Vol. 2 page 344]

• And from those who are not on the path of Muhammad’s progeny pbut: Al-Thalabi narrated in the interpretation of what the Almighty said,
﴾Pearls and coral come out from both of them.﴿, that Sufyyan AlThori said, “They are Fatima and Ali pbut,” ﴾Pearls and coral come out from both of them.﴿ he said, “Al-Hassan and Al-Hussein pbut.” Al-Thalabi said, “And this was narrated from Saeed bin Jubeir,
and he said, ‘﴾There is a barrier between them﴿ Muhammad pbuhap.’ ” [Al-Burhan Vol. 27 chapter 7 page 389.]

The Journey of Moses pbuh to the Junction of the Two Seas
http://saviorofmankind.com/images/stories/pdf/journeymoses.pdf

قال الامام احمد الحسن ع
أما الروايات التي بينت أن البحرين هما علي وفاطمة، وإن ما يخرج منهما وما يجري فيهما هم الأئمة والمهديون (ع) فهي كثيرة، وهذه منها:
عن أبي عبد الله (ع) قال في قول الله تبارك وتعالى: ﴿مَرَجَ الْبَحْرَيْنِ يَلْتَقِيانِ بَيْنَهُما بَرْزَخٌ لا يَبْغِيانِ ﴾، قال: (علي وفاطمة بحران عميقان لا يبغي أحدهما على صاحبه، ﴿يَخْرُجُ مِنْهُمَا اللُّؤْلُؤُ وَالْمَرْجانُ﴾ قال: الحسن والحسين عليهما السلام)
تفسير القمي: ج2 ص244.

رحلة موسى إلى مجمع البحرين
http://almahdyoon.org/pdf/36-maktaba/kotob-alimam-ahmad-alhassan/10117-ri7latmossa