This quote comes right after Roger has killed Piggy by rolling the boulder off the top of Castle Rock onto Piggy. Piggy's death was preceded by a yelling match between Piggy and Jack where Piggy asked the boys of Jack's tribe, which was better - to be sensible or to be a pack of painted Indians? Piggy's death was sudden and swift. He is crushed and washed away and in that same moment, reason and civility are also washed away by the ocean. Once Piggy's body was gone, the water quickly went from pink to white again like the death never occurred. Once Piggy is dead and all reason is gone, it's almost as if reason and civility had never occurred on the island. The correlation between the ocean's washing away of Piggy's body and the savagery on the island being complete is clear.