While watching One Piece I noticed that Nami's voice sounded different coming into the Little Garden arc. When I looked up info on her character on the One Piece wiki I found that during episodes 70-78 she had a different Japanese voice actress, Wakana Yamazaki, before returning to the previous voice actress, Akemi Okamura. I can't seem to find any reason or explanation for this. Does anyone have a clue why this would be? It was all part of a canon arc too.
According to Nami's Wikipedia's page:
In the Japanese version of the entire One Piece anime series, and later spin-offs, Nami has been voiced by Akemi Okamura. In 2001, Okamura temporarily left the series due to her pregnancy; Wakana Yamazaki acted as a substitute for episodes 70-78.