How did Huck know Pap wasn't drowned?

Can you please elaborate on how Huck Finn in the novel "The Adventures of Huckleberry Finn" by Mark Twain came to the conclusion that his father, Pap, had not drowned? Did he witness something specific that suggested Pap's survival? Or was it a series of clues and observations that led him to this belief? Additionally, did Huck have any prior knowledge of Pap's swimming abilities or survival skills that might have influenced his conclusion? It would be interesting to understand the reasoning behind Huck's certainty that Pap was still alive.