I've done a little digging - initially trying to read the message on
this lady's back, but it is just a regular prayer (Hail to the Virgin Mary, the Father, the Son and the Holy Ghost etc etc).
However I did find out that there is another festival that involves baptism that takes place on July 28th - the Baptism of the Rus' when the ancestor state of the Russian-speaking states was Christianised.
It isn't necessarily associated with voluntary immersion the way Epiphany is but it's a popular day for mass baptisms - though the pictures I found all involved a priest. Could it be this is a celebration of that anniversary rather than the winter Epiphany?