Hydna was well known in Greece as a skilled swimmer, having been trained by her father, a professional swim instructor named Scyllias( Scyllias was from Skiony, a small polis on the Chalkidiki peninsula. According to Herodotus, - the best diver of his time) from a young age. Hydna was known for her ability to swim long distances and dive very deep into the ocean.  In his narrative, Herodotus tells us about the episode with the diver Scyllias, who, together with his daughter Hydna, volunteered to assist Greek forces by vandalizing the nearby Persian naval fleet underwater, that happened before the naval Battle of Artemisium (a naval battle between the Greek and Persian fleets during the Greco-Persian Wars , which occurred in 480 BC in the narrow straits between the island of Euboea and the mainland of Greece at Cape Artemisium). On the night of the attack, father and daughter swam roughly ten miles through rough, choppy waters to reach the ships. They silently swam among the boats, using knives to cut the moorings and dragging away the submerged anchors. Without anchors and moorings to secure the ships, they crashed together in the stormy water. Most of the ships sustained considerable damage and a few sank. The resulting delay allowed the Greek navy more time to prepare in Artemisium and ultimately led to a victory for Greek forces at Salamis.