Very useful article, thank you. It seems from it that it would be best not to take him to a public swimming area that unknown dogs frequent until he has completed puppy shots, around 12 weeks.Going to post this article:
Striving for Puppy Wellness:
Are Early Socialization and Infectious Disease Prevention Incompatible
http://www.apdt.com/veterinary/assets/pdf/Messer_ND06.pdf