Dawn Fraser was the only female swimmer I could find. There were no quotes from Janet Evans, Natalie Coughlin et al. What a shame too.
These quotes don't offer much in the way of wisdom but it gives you a sense about how they view themselves and competition.
Michael Phelps quotations page: Link
Ian Thorpe quotations page: Link
Mark Spitz quotations page: Link
Dawn Fraser quotations page: Link
Here is my favorite quote from Johnny Weissmuller, the first person to break a minute in the 100 meter free and later made a fortune playing Tarzan in the movies:
"Throughout my career I swam for form. Speed came as a result of it."