Princess Tressa is the princess of the mermaids and tritons. She is the daughter of Queen Ligea and King Neptune. She has twin brothers Nereus and Tritannus and she is the heir to the mermaid throne. She is also Aisha's cousin. When Valtor invaded Andros, Tressa was able to avoid capture but mainly due to phobia. When she escaped, she went looking for Aisha and eventually found her and the Winx. Aided by the Winx, she rescued her mother and saved Aisha from the Kraken.
She has spiked red hair that is tied in a ponytail, and eyes that are similar to the color orange. She is mermaid so she has sort of a purplish-blueish tail. Unlike the other mermaids, her tail is similar to a fish. Her wings have dark blue, dark orange and dark yellow parts with black lines.
She looks identical to Tritannus' other mutants in which her build becomes skinny, has an ill colored skin tone with many wrinkles to her face and transparent flaps beneath her arms.
At first, Tressa was shown to be rather fearful and she herself admitted it. But she is just as brave and determined when the people she cares for are in danger. In Season 5, it seems that her bravery has improved and she is willing to defend her kingdom, as shown when Tritannus tried to ambush Nereus, she wield the nearest weapon and shouted "traitor". She also greatly loves her parents as she declared to the Sovereign's Council that their main objective should be freeing her parents. She is also skilled in swordsmanship.
Her first appearance is in episode 6. She asks for Aisha's help in freeing her mother, who was imprisoned by Valtor. She leads Aisha and the Winx Club to the Kraken's cave and opens her mother's jail cell. After narrowly escaping the Kraken's cave, her mother volunteers the use of her staff that contains a coral stone on top to cure Aisha's blindness, but they must catch the last rays of the sun. As they hurry to do so the monster hits Tressa's mother, fatally injuring her. Tressa comes to her rescue and finds out that she is dying. The Winx help Tressa bring her to the surface and Aisha uses the coral stone to save Tressa's mother, gaining her Enchantix.
In Season 5, Tressa is shown to be speaking to Aisha over a video chat, showing the Winx the ceremony of one of the princes claiming the crown and title as king. When Tritannus attacks Nereus, the chat session ends, leaving the Winx in confusion. On Andros, it is revealed that Tritannus had disrupted the ceremony; Tressa being one to act, wanted to fight the masked man (Tritannus), but her mother Queen Ligea told her to protect her brother. Some time later, she along with King Neptune are turned into mutant mer-monsters. Later on in The Eclipse, she and Nereus are restored to their original forms by Aisha using King Neptune's sword. After being restored, she and her brother attended the Sovereign's Council in an effort to convince the other kingdoms to unite and fight together against Tritannus but to no avail. However, after much debate the kingdoms finally unite and set their course for Tritannus' defeat. When Tritannus finally activated the Emperor's throne he sent his mutants to Andros, Tressa and the Winx, minus Bloom, followed them and fought their best against the mutants. And soon enough, Tritannus is defeated and the mutants returned to normal. Tressa is then finally united with her parents and she attends Andros' party with her family.
- Tressa's Nickelodeon voice actor also provides voice for Serena and Matlin.