5 snorkeling highlights around Marathonisi, starting from Keri

Not many places in Greece offer the magic of Zakynthos, an island where turquoise waters meet dramatic cliffs, and sea turtles glide silently beneath the surface. Among its natural treasures, Marathonisi Island stands out as a true gem, not just for its breathtaking beauty, but for the incredible snorkeling experience it offers around its shores. Known as “Turtle Island”, Marathonisi is part of the protected National Marine Park of Zakynthos and serves as a key nesting ground for the endangered loggerhead sea turtle (Caretta caretta).

But getting to this turtle haven isn’t just a matter of hopping on a boat; the journey is part of the experience. The best way to reach Marathonisi is to drive to the charming village of Keri, located on the island’s southwest coast. From there, a short boat ride transports you into the heart of some of the most biodiverse and crystal-clear waters in the Ionian Sea.

This article guides you through that adventure: from the scenic drive to Keri, to what awaits under the water once you arrive near Marathonisi. We’ll cover five unforgettable snorkeling highlights, the best time to visit for turtle sightings, and practical tips for making the most of your trip, whether you’re traveling solo, as a couple, or with family.

Driving to Keri

To experience the magic of Marathonisi Island, your journey begins on the road, specifically, the scenic drive to the peaceful coastal village of Keri, located on the southwest tip of Zakynthos. While Laganas is a more popular (and often crowded) departure point, Keri offers a quieter, more authentic gateway to the turtle haven. This makes it the ideal choice for travelers seeking a relaxed, self-paced adventure.

From Zakynthos Town, the drive to Keri takes approximately 35-40 minutes by car, winding through a mix of olive groves, pine forests, and traditional stone villages. Along the way, you’ll pass through rural landscapes dotted with local tavernas, goat farms, and panoramic viewpoints that beg for a photo stop. Renting a car gives you the flexibility to pause, explore, and take in the surroundings on your terms, an experience that packaged tours simply can’t offer.

As you approach the coast, the road descends toward Keri Beach (Limni Keriou), a quiet seaside area with calm waters, a few laid-back restaurants, and a small harbor. This is where you’ll find several local boat rental services and tour operators offering access to Marathonisi Island. Whether you choose a guided boat tour or prefer to rent a small motorboat and explore independently, Keri is well-equipped for both. Most boats don’t require a license, and staff will provide brief safety instructions before departure.

Parking at Keri is typically free and relatively easy compared to busier spots like Laganas. It’s recommended to arrive early in the morning during peak season (June to September), as the small lot near the beach can fill up quickly. After securing your spot, you can grab a coffee or light snack at one of the beachside cafés before heading out on the water.

Driving to Keri isn’t just a way to reach Marathonisi; it’s part of what makes the experience special. The peaceful vibe, scenic coastal road, and flexibility of a self-drive trip all add to the sense of freedom that defines this side of Zakynthos. For travelers seeking to escape the crowds and explore the island’s natural treasures on their schedule, renting a car and driving to Keri is the perfect start.

Exploring the waters of Marathonisi

Once you’ve launched from Keri and set your sights on Marathonisi, it quickly becomes clear why this small, uninhabited island is one of Zakynthos’ most celebrated natural wonders. Surrounded by crystal-clear waters in varying shades of blue and turquoise, Marathonisi offers a snorkeling environment that feels untouched and wild; a stark contrast to the more developed tourist beaches found elsewhere on the island.

Marathonisi sits just a short boat ride from Keri, rising gently from the sea like a green dome. Its shape has often been compared to that of a turtle, which only adds to its charm and nickname: “Turtle Island”. While visitors are not allowed to set foot on the main beach during the nesting season (typically May through October), the waters around the island remain open for exploration and are teeming with life.

The most iconic residents here are the loggerhead sea turtles (Caretta caretta). These gentle creatures can often be spotted near the surface, gliding slowly through the water or rising for a breath of air. Strict conservation rules protect them, so swimmers and snorkelers are advised to keep a respectful distance and avoid approaching or disturbing them. Nevertheless, it’s common to encounter turtles while snorkeling around the island, making it one of the top wildlife experiences in Zakynthos.

The underwater landscape around Marathonisi is just as impressive. On one side, you’ll find shallow areas with seagrass meadows, a key habitat for turtles and smaller fish. On the other side, the terrain becomes more rugged, with rocky outcrops, caves, and overhangs that create shelter for various species of marine life. The water here is remarkably clear, often offering visibility of 20 meters or more, allowing you to see colorful fish, sponges, and sometimes even octopuses hiding in the rocks.

Due to the marine park’s regulations, large boats are prohibited from anchoring too close to the island, which keeps the environment calm and less trafficked than other parts of the coast. Most snorkeling spots are accessible directly from small rental boats, and many visitors choose to stop at several locations around the island’s perimeter to explore different underwater features.

Whether you’re an experienced snorkeler or a complete beginner, the waters around Marathonisi offer a rare opportunity: the chance to immerse yourself in nature, observe endangered wildlife in their habitat, and feel like you’ve stepped into a different world, all just a short boat ride from Keri.

5 snorkeling highlights around Marathonisi island

Snorkeling around Marathonisi isn’t a one-note experience — the island offers a range of underwater landscapes and wildlife encounters that vary by location. Here are five standout snorkeling spots and experiences that make this area a true marine adventure.

1. The loggerhead turtle passage

The shallow waters just offshore on the northwestern side of Marathonisi are often patrolled by Caretta caretta, especially in the early morning or late afternoon when boat traffic is minimal. This area is part of the official nesting zone, so while you can’t step onto the beach during turtle season, you can snorkel respectfully nearby and observe these majestic animals in their natural environment. With some patience, you’ll likely spot a turtle gliding gracefully just beneath the surface. It’s a quiet, surreal experience, the kind that leaves a lasting impression.

2. The seagrass meadows near the island’s base

On the southern and southeastern flanks of the island, you’ll find dense seagrass beds just a few meters below the surface. These underwater meadows are vital to the local ecosystem, serving as feeding grounds for turtles and shelter for small fish, eels, and invertebrates. Snorkeling here is less about dramatic rock formations and more about subtle detail: watch for movement between the grasses, spot schools of silver fish, and float peacefully above an underwater prairie. The seagrass sways gently with the current, creating a calm and mesmerizing setting.

3. Cave snorkeling on the rocky western shore

The western side of Marathonisi features a rugged, cliff-like shoreline with shallow caves and crevices that are perfect for snorkeling. Some of these sea caves extend several meters into the rock, allowing snorkelers to explore just inside the entrances where sunlight filters through the water, illuminating the walls in vibrant blue hues. These rock formations offer a home to more elusive marine life, like octopuses and spiny sea urchins. It’s one of the more adventurous parts of the island’s perimeter, so be sure to wear fins and stay close to your boat if you’re not a strong swimmer.

4. Colorful fish zones on the eastern edge

While Marathonisi is best known for turtles, it also offers surprising biodiversity. The eastern edge of the island features scattered rocky platforms and coral-like formations where bright fish like damselfish, rainbow wrasse, and parrotfish are frequently spotted. This area is shallow and ideal for beginner snorkelers or families, as the terrain is easier to navigate and the sea is usually calm. Bring a waterproof camera if you have one: the fish here are curious and colorful, often swimming just a few meters away.

5. Hidden coves accessible by small boat

Perhaps the most rewarding snorkeling experiences around Marathonisi occur in the quiet coves, only accessible by small motorboat. These tucked-away corners offer calm water, minimal traffic, and an extra layer of privacy. Some coves are surrounded by sheer limestone walls, creating a sheltered, echoing space where even the sound of your breath underwater becomes part of the experience. These spots are ideal for floating in silence, soaking in the scenery, and spotting marine life away from the more visited areas. The isolation here gives a sense of discovery, as if you’ve found your secret corner of the Ionian Sea.

Best time to visit for snorkeling and turtle sightings

Choosing the right time to visit Marathonisi can make the difference between a pleasant swim and a once-in-a-lifetime wildlife encounter. While Zakynthos is beautiful year-round, the ideal months for snorkeling and spotting turtles are closely tied to weather conditions, water clarity, and the turtles’ natural nesting cycle.

Turtle nesting season

Marathonisi is part of the National Marine Park of Zakynthos, a protected zone established to safeguard the loggerhead turtle’s nesting grounds. The official nesting season runs from May through October, with the highest concentration of turtles between June and August. During these months, female turtles come ashore at night to lay eggs on the protected beach of Marathonisi, and it’s common to see them swimming in the surrounding waters during the day.

If your main goal is to see turtles, plan your visit between late June and early August, when the water is warm and calm, and turtle activity is at its peak. Just remember: this is also high season, so it’s wise to arrive early in the day to avoid boat traffic and find a good parking spot in Keri.

Snorkeling conditions from May to October

The snorkeling season mirrors the turtle season. Water temperatures start to warm in May and remain ideal through October, typically ranging from 22°C to 28°C (72°F to 82°F). Visibility is excellent in summer, often over 20 meters, especially on clear, windless days. From July onward, sea conditions are usually calm and stable, offering the best environment for a relaxing snorkeling experience.

Avoiding crowds: May, September, and Early October

For a quieter experience, consider visiting in May, September, or early October. While you may see fewer turtles, the weather is still pleasant, the water remains warm, and the snorkeling conditions are excellent, with far fewer boats and tourists in the area. These shoulder-season months are ideal for couples or solo travelers looking for a peaceful, immersive connection with nature.

Practical tips for a safe and memorable snorkeling trip

Snorkeling around Marathonisi is one of the most rewarding experiences Zakynthos has to offer, but to make the most of it, it’s important to come prepared. From choosing the right type of boat to understanding marine park rules, these practical tips will help ensure your adventure is smooth, safe, and respectful of the fragile ecosystem.

1. Choose the right boat for your needs

From the port of Keri, you’ll have two main options: renting a small self-drive boat or joining a guided boat tour. For those who value flexibility and privacy, a rental boat is a fantastic choice; most don’t require a license, and rental companies offer short training sessions to get you started. If you’re less confident on the water or want a local guide to point out turtle sightings and ideal snorkeling spots, consider booking a small-group tour with a local operator.

2. Bring your snorkeling gear (if you can)

While some boat rental shops or tour providers may offer snorkeling gear, the quality and fit can vary. For hygiene and comfort, it’s a good idea to bring your mask, snorkel, and fins,  especially if you plan to explore multiple areas. A lightweight dry bag and waterproof phone case are also useful for storing valuables on board.

3. Respect marine life and park regulations

Marathonisi is located within the protected Zakynthos Marine Park, and visitors must follow strict guidelines. Never touch or feed sea turtles or other marine creatures. Keep a distance of at least 10 meters from any turtle you spot. Avoid stepping onto the nesting beach during turtle season, and do not anchor your boat near sensitive areas. Rental companies will advise where it’s permitted to stop.

4. Time your visit wisely

To beat the crowds and increase your chances of seeing turtles, aim to arrive at Keri Beach before 10:00 AM, especially in July and August. Morning hours tend to have calmer seas and better visibility for snorkeling. If you’re visiting in the afternoon, prepare for more boat traffic and potential waves stirred up by the wind.

5. Stay hydrated and protect yourself from the sun

The Greek sun can be intense, especially when you’re out on the water for several hours. Bring plenty of water, wear reef-safe sunscreen, and use a wide-brimmed hat or UV-protective clothing. Avoid using oily sunscreens that harm marine life, opt for biodegradable products labeled “reef safe”.

6. Be mindful of boat safety

Whether you’re renting a boat or joining a tour, safety should come first. Ensure your boat has a ladder for easy re-entry, a buoy or anchor, and a first aid kit. Let someone on shore know your planned return time, and never venture too far from the island unless you’re with a guide or experienced boater.

What truly elevates this trip is the freedom of having your wheels. Renting a car in Zakynthos gives you the flexibility to explore beyond the usual tourist routes, avoid the crowds, and reach places like Keri on your schedule. It’s what turns a simple beach day into a full-day island adventure, complete with scenic stops, hidden tavernas, and the ability to linger at your favorite snorkeling spot without watching the clock.

So pack your mask, book your car with Top Rentals, and drive to Keri at your own pace. With pickup right at the airport or the town, your turtle adventure begins the moment you turn the key. Skip the crowded tours, explore Zakynthos your way, from the open road to the crystal waters of Marathonisi.