When Odysseus visits the Land of the Dead, Tiresias tells him he will die a "seaborne death." No further details are provided. When Odysseus returns to Ithaca and restores after taking care of the suitors, he must make peace with Poseidon. Tiresias tells him to take an oar and go so far inland that no one recognizes the implement; they think it is a "winnowing fan," a farm tool used for separating wheat from chaff. At that point Odysseus is to plant the oar and make certain sacrifices to Poseidon to end their feud. After that time Odysseus will apparently live a long life before his predicted death at sea.
The audience of the Odyssey, which was originally an oral epic poem, would have known how the mythical Odysseus really did die. In the poem, which the blind prophet Tiresias tells him that he will die a death from the sea, no other information is immediately given.
The audience would have known that this was a reference to his death from his son. During his travels, he was captured by the sea-witch Circe. When he left, Circe was pregnant, but he had no knowledge of it. She gave birth to their son, named Telegonus, who grows to manhood without him.
Many years later, after his safe return to Ithaca and Penelope and Telemachus, he is living in happiness. However, his son Telegonus has decided that he really wants to meet his long-lost father. Telegonus sets out to sea in search of him, and actually ends up on Ithaca. When he arrives, he is desperately hungry, so he kills some of the Ithacan sheep to feed himself. From the palace above the beach, Odysseus sees this happening. He thinks that Telegonus is a pirate and thief, and goes down to confront him and drive him away. Odysseus and Telegonus start fighting. Neither of them know who the other is. Finally, Odysseus is killed by Telegonus's spear, which is tipped with poison from a sting ray.
Tiresias's prophecy really does come true--his death comes from the sea.