A.T. Robertson Commentary Mark 1:5

"And there went out unto him all the country of Judaea, and all they of Jerusalem; And they were baptized of him in the river Jordan, confessing their sins." — Mark 1:5 (ASV)

Then went out unto him (εξεπορευετο προς αυτον). Imperfect indicative describing the steady stream of people who kept coming to the baptism (εβαπτιζοντο, imperfect passive indicative, a wonderful sight).

In the river Jordan (εν τω Ιορδανη ποταμω). In the Jordan river, literally.