John 1:25 questions

[christianmomof3]

25 And they asked him and said to him, Why then are you baptizing if you are not the Christ nor Elijah nor the Prophet?

I have some questions about this verse.
Apparantly, John was baptising people in a river.
This was not, to my understanding, a practice of the Jewish religion at that time.
As far as I know, there were ritual baths called Mikvah's, but they were done to oneself and not by anyone to someone.

So, the first question, was the baptism that John was doing something entirely new to the Jewish people?

Then, the second question - why did they think that because John was baptising people he must have been Christ, or Elijah or the Prophet?
Where did that concept come from?

 

[texastig]

From: WikiAnswers - Why did John the Baptist baptize Jews

John's baptism was an adaptation of the mikvah, or ritual immersion bath, that had been part of Jewish life for generations and symbolized a spiritual cleansing. It was used to consecrate a new beginning. Jewish men took a mikvah each Sabbath. Women took a mikvah after each monthly period. On Yom Kippur the High Priest took 7 mikvot (plural of mikvah) during the ceremonies. Jesus came to John for a mikvah at the beginning of His ministry.
The reason John had people take a mikvah was to show that they had changed their minds (repented) about their need for a Savior and were taking a new direction regarding their salvation. No longer would they focus on keeping the Law but would look instead to the coming redeemer whose arrival John was announcing. Once Jesus came, John's baptism of repentance was no longer needed, so it became a symbol of the believer's death and re-birth. (Why Did John Baptize People? | GraceThruFaith)

The reason why I think they thought he was a prophet or Elijah was because of his intense preaching.

Thanks,
TT