I don't get this joke...?!

I don't get this joke...?

Will you tell me how this joke it funny?

A White Guy And a Black Guy were walking home after a night in the pub.
As they approached a river the White guy turned to the Black Guy and
said it,s no good iv'e gpot to take a pee. Yep said the Black guy so
have I.They both turned towards the river and started to pee. After a
few seconds the White guy turned to the Black guy and said ,this bloody
water is cold. Yep said the Black Guy it's bloody deep to.

I got this from an email in a group:
groups.yahoo.com/group/so_funn...

It is a gross joke. The white guy was saying that is was cold water because could felt it. And the black guy was saying that is was deep because he was "bigger."
It is kind of funny, but a little gross too.