There are no pok�mon in the water when surfing from pallet Town to Connibar and back. I'll say:
Tangela (in the grass patch just below Pallet Town)
Vulpix
Rattata
Raticate
Grimer
Koffing
Muk
Weezing
Magmar
Ditto
Those are all the ones I've encountered between and on these areas INCLUDING the Pok�mon Mansion. I think there might be more, I'm not sure.
I'm finished here...
Special thanks to Yossy666 for the avatar and signature images.