7:1-10:
7:21-28:After these things, during the reign of Artaxerxes king of Persia, Ezra son of Seraiah, the son of Azariah, the son of Hilkiah, the son of Shallum, the son of Zadok, the son of Ahitub, the son of Amariah, the son of Azariah, the son of Meraioth, the son of Zerahiah, the son of Uzzi, the son of Bukki, the son of Abishua, the son of Phinehas, the son of Eleazar, the son of Aaron the chief priest— this Ezra came up from Babylon. He was a teacher well versed in the Law of Moses, which the Lord, the God of Israel, had given. The king had granted him everything he asked, for the hand of the Lord his God was on him. Some of the Israelites, including priests, Levites, musicians, gatekeepers and temple servants, also came up to Jerusalem in the seventh year of King Artaxerxes.
Ezra arrived in Jerusalem in the fifth month of the seventh year of the king. He had begun his journey from Babylon on the first day of the first month, and he arrived in Jerusalem on the first day of the fifth month, for the gracious hand of his God was on him. For Ezra had devoted himself to the study and observance of the Law of the Lord, and to teaching its decrees and laws in Israel.
8:15-23:... Ezra the priest, the teacher of the Law of the God of heaven ... you, Ezra, in accordance with the wisdom of your God, which you possess, appoint magistrates and judges to administer justice to all the people of Trans-Euphrates—all who know the laws of your God. And you are to teach any who do not know them ... Praise be to the Lord, the God of our ancestors, who has put it into the king’s heart to bring honor to the house of the Lord in Jerusalem in this way and who has extended his good favor to me before the king and his advisers and all the king’s powerful officials. Because the hand of the Lord my God was on me, I took courage and gathered leaders from Israel to go up with me.
9:1-4:I assembled them at the canal that flows toward Ahava, and we camped there three days. When I checked among the people and the priests, I found no Levites there. So I summoned Eliezer, Ariel, Shemaiah, Elnathan, Jarib, Elnathan, Nathan, Zechariah and Meshullam, who were leaders, and Joiarib and Elnathan, who were men of learning, and I ordered them to go to Iddo, the leader in Kasiphia. I told them what to say to Iddo and his fellow Levites, the temple servants in Kasiphia, so that they might bring attendants to us for the house of our God. Because the gracious hand of our God was on us, they brought us Sherebiah, a capable man, from the descendants of Mahli son of Levi, the son of Israel, and Sherebiah’s sons and brothers, 18 in all; and Hashabiah, together with Jeshaiah from the descendants of Merari, and his brothers and nephews, 20 in all. They also brought 220 of the temple servants—a body that David and the officials had established to assist the Levites. All were registered by name.
There, by the Ahava Canal, I proclaimed a fast, so that we might humble ourselves before our God and ask him for a safe journey for us and our children, with all our possessions. I was ashamed to ask the king for soldiers and horsemen to protect us from enemies on the road, because we had told the king, “The gracious hand of our God is on everyone who looks to him, but his great anger is against all who forsake him.” So we fasted and petitioned our God about this, and he answered our prayer.
No one seems to know exactly where the Ahava Canal was though, but a comment on the biblehub says:After these things had been done, the leaders came to me and said, “The people of Israel, including the priests and the Levites, have not kept themselves separate from the neighboring peoples with their detestable practices, like those of the Canaanites, Hittites, Perizzites, Jebusites, Ammonites, Moabites, Egyptians and Amorites. They have taken some of their daughters as wives for themselves and their sons, and have mingled the holy race with the peoples around them. And the leaders and officials have led the way in this unfaithfulness.”
When I heard this, I tore my tunic and cloak, pulled hair from my head and beard and sat down appalled. Then everyone who trembled at the words of the God of Israel gathered around me because of this unfaithfulness of the exiles. And I sat there appalled until the evening sacrifice.
In Ezra 8:15 the river is designated אל־אהוא הבּא, i.e., either which comes (flows) towards Ahava, or flows into Ahava; in Ezra 8:21 it is more briefly called אהוא נהר, and in Ezra 8:31 אהוא נהר, which may mean the river of Ahava, of the region or district called Ahava, or, after the analogy of פּרת נהר, merely the river of the name of Ahava. It is doubtful which of these meanings is correct, the name Ahava being still unexplained. Comp. the various conjectures in A. G. F. Schirmer, observationes exeg. crit. in libr. Esdrae, Vratisl. 1820, p. 28ff. The connection points to a place or district in the neighbourhood of Babylon; hence Bertheau is inclined to regard Ahava as a tributary or canal of the Euphrates, flowing through a place, perhaps only a field or open space, of the same name, in the immediate neighbourhood of Babylon; while Ewald supposes it may be the river somewhat to the west or south of Euphrates, called by the Greeks Pallacopas, whose situation would suit the context, and whose name might arise from אהוא פלג, the river Ahwa or Aba. The lxx gives the name Εὐί; in 1 Esdr. 8:40 and 61 we find Θερά, evidently a false reading. Josephus says quite generally, εἰς τὸ πέραν τοῦ Εύφράτου.
http://biblehub.com/commentaries/ezra/8-21.htm