Hydrousa Island: The Hidden Gem Across from Kavouri

Hydrousa (also known as Katramonisi or Prasonisi) is a small, uninhabited island located in the Saronic Gulf, directly across from the popular beach area of Kavouri, near Voula and Vouliagmeni in southern Athens. The island lies approximately 0.7 nautical miles (around 1.1 kilometers) from the coast of Voula and covers a total area of about 57,000 square meters.

The name “Hydrousa” was historically used in ancient Greece to refer to several Aegean islands, including Kea and Tinos. In modern times, this specific islet has also been known as “Katramonisi” and “Prasonisi.” Despite its small size, the island has a fascinating backstory involving World War II fortifications and legal disputes over private ownership.

Natural Features and Beaches

Hydrousa boasts two small beaches, each with crystal-clear waters and a mix of sand and pebbles. The northern beach is the most frequently visited, offering some natural protection from the wind due to an offshore reef. It is a popular anchoring point for private boats and yachts, especially during weekends. The southeastern beach is more remote and exposed, ideal for those seeking solitude.

Wildlife and Landscape

The island is famous for its wild rabbits, which roam freely and often approach visitors. This charming detail has become one of its most recognizable characteristics. The surrounding waters are home to rich marine life, including dolphins, rays, and octopuses, making it an appealing stop for snorkelers and divers.

Underground WWII Shelter

One of the island’s most intriguing features is an underground bunker, believed to have been built during World War II. The shelter includes tunnels, storage chambers, ventilation shafts, and a hidden “balcony” area. Parts of the system also housed machine gun nests, located approximately 8 meters below the surface. It adds an unexpected historical depth to the otherwise serene environment.

Ownership and Legal History

Hydrousa’s ownership has been the subject of legal battles. Initially under state claim, the island’s rights were eventually awarded to a private citizen—not a wealthy magnate, but a bus driver—after prolonged court proceedings. In recent years, there were controversial plans for light tourism development, including floating canteens and wooden sunbeds, but these efforts were halted due to environmental and legal concerns.

Access and Recommendations

There is no ferry or organized transportation to Hydrousa. Access is only possible by private means—via inflatable boats, kayaks, jet skis, or small vessels from Kavouri, Voula, or Vouliagmeni. Due to high visitor traffic on weekends during the summer, weekdays are strongly recommended for a more peaceful experience.

• Distance from shore: ~0.7 nautical miles from Voula
• Area: ~57,000 m²
• Beaches: 2 (North: protected, popular; Southeast: isolated)
• Wildlife: Wild rabbits, rich marine fauna
• WWII feature: Underground shelter with tunnels and gun posts
• Legal status: Privately owned after lengthy litigation
• Access: Only by sea—no official transport
• Best time to visit: Weekdays, especially outside peak season

Hydrousa remains one of the few untouched and mysterious places near the Athens Riviera. Despite its proximity to urban life, it offers raw beauty, unexpected history, and a sense of peaceful escape—a true hidden gem of the Saronic Gulf.

🏛️ Historical Use of the Name

• Kea (also known as Tzia) was referred to as Hydrousa or Hydroussa by ancient authors, mainly because of its numerous springs and its relative fertility compared to other Cycladic islands.
• Tinos has also been mentioned in certain texts as Hydrousa, primarily in ancient descriptions connected to water-related rituals, the island’s abundant springs, and its agricultural richness.
• The name Hydrousa was not exclusive to a single island but appears to have been used as a descriptive geographic term for islands with abundant water resources or rich natural features.

🧭 What is its connection to the modern Hydrousa (Katramonisi)?

Today’s Hydrousa, located opposite Kavouri, likely received its name symbolically or by analogy with these ancient uses. Even though it is small, it has relatively dense vegetation and some underground moisture by Saronic Gulf standards — features that may have inspired the name.

📚 Sources & References

• Strabo, Geographica
• Pausanias, Description of Greece
• The lexicons of Hesychius and Stephanus of Byzantium (entries under “Hydrousa”)
• Toponymic and historical lexicons of the Cyclades and the Saronic Gulf