When one immerses in the mikveh, it is customary to recite blessings. A sample of  the blessings recited for conversions is included below.  

Blessings for Immersions:

Barukh atah Adonai, eloheynu melekh ha-olam, asher kid-shanu b'mitz'votav, v'tzi-vanu al ha-t'vilah.
Blessed are You, Adonai, our God, Ruler of the Universe, who has made us holy with Your mitzvot including the mitzvah of immersion. 

Barukh atah Adonai, eloheynu melekh ha-olam, sheh-heh-hi-yanu v'kiy-manu v'hi-gi-anu laz'man hazeh. 
Blessed are You, Adonai, our God, Ruler of the Universe, who has given us life and sustained us, and enabled us to reach this sacred day.

Sh'ma Yisrael, Adonai eloheynu, Adonai ehad.
Hear, Israel, Adonai our God, Adonai is One. 

The blessings can also be found at the following link:  Blessings for Immersions