SOAK is Bridie Monds-Watson, a folk singer from Derry in Ireland. This song is about a friend of hers who was being heavily bullied. "The only way for her to strike back was by calling the other girl a whale, in her head," she explained to NME.
Despite the song's childlike lyrics, there is darkness bubbling under the surface. Originally "fish" was "bitch," but SOAK changed it on the basis of radio play.
"Whole Lotta Love" was Led Zeppelin's only US Top 10 hit, charting at #4. Many of their songs, including "Stairway To Heaven," were not released as singles, as it was considered bad form in England to make people pay for singles that were on albums.