The sea temperatures around Kefalonia vary significantly throughout the year due to its Mediterranean climate, and these changes influence the experience for swimmers, marine life, and coastal activities. The actual weather of Kefalonia and the sea currents define also the waters of the area, and it’s worth to know that the temperatures at many beaches can differ significantly from each other due to their location.
Kefalonia Island sea temperatures are pleasant from June to the end of September for a holiday in Greece, but there are a lot of things and local informations, which are good to know. Now let’s see a month-by-month breakdown of typical sea temperatures in Kefalonia during the year. It’ very important to know the sea temperatures of Kefalonia before a holiday, because you can choose easily the best weeks for traveling to the island!

January
In January, the waters around Kefalonia are at their coldest, as winter is in full swing. The average sea temperatures of Kefalonia Island in January hover around 15°C (59°F). This temperature can feel very cold, especially for swimming. Though the island itself is relatively mild during winter, the sea takes longer to heat or cool due to its high thermal inertia. Consequently, January’s waters feel brisk, and choose other options for other seasonal activities instead of swimming.
February
February sees a slight drop or stabilization in sea temperature of Kefalonia, typically remaining around 14-15°C (57-59°F). In February the sea water is still very cold by swimming standards, so forget swimming due to cold sea temperatures and to strong currents of the sea. Marine life is also less active due to the colder conditions.
March
As spring approaches, sea temperatures in March start to show a subtle increase near Kefalonia island in Greece, with the average ranging from 15°C to 16°C (59-61°F). Although still very cool, the warming trend begins, particularly during sunny afternoons. Sea temperatures of March remains cold for typical beach activities in Kefalonia.

March also brings slightly more marine activity, with fish and other species becoming slightly more active as temperatures slowly rise. Due to the weather in the month of March is not recommended for swimming due to sea temperatures, but it can be great for hiking or discovering the local attractions.
April
April brings more noticeable warmth to the sea, with average temperatures around 16-18°C (61-65°F). This is a turning point as the sea becomes slightly tolerable for swimming for a few, though it still feels very cold for most people. Locals and early tourists may start enjoying shorter swims, although you must prefer wetsuits for prolonged immersion.

April’s rising temperatures also mark an increase in marine life visibility, attracting underwater enthusiasts. If you travel to Kefalonia Island in Greece in April, keep in mind that sea temperatures in are low yet, and we suggest hiking instead of swimming.
May
By May, Kefalonia’s sea temperatures rise further, reaching an average of 18-21°C (64-69°F). This is where the sea starts to feel comfortable for some swimmers, especially during warmer days, but for most people these temperatures are cold.

The island also sees an increase in tourism, as more visitors are willing to enter the sea without the need for protective wetsuits. May’s temperature, though still on the cooler side, support the outdoor activities, and in shallow bays (Xi beach, etc) you can try swimming. The warmer waters also encourage marine biodiversity, making snorkeling and diving popular as the waters become teeming with marine life.

The locals deploy the first parasols and sunbeds in May to the Kefalonian beaches.
June
June marks the beginning of summer for Kefalonia, with sea temperatures averaging 21-24°C (70-73°F). This temperature range is generally considered ideal for most swimmers due to the pleasant weather of June, with a nice balance between coolness and warmth.
From the middle of June the sea is fully inviting for swimming, snorkeling, and other water activities, often without the need for any thermal wetsuit. In the first two weeks of June sea temperatures can be varied due to actual weather conditions, but if you spend your holiday at this time, don’t forget to bring your swimsuit!

By late June, the sea may even reach higher temperatures in shallower, sun-exposed bays, creating perfect conditions for family-friendly swimming, beachgoers, and marine excursions. The warmer waters also bring out the full spectrum of marine life, making it a vibrant time for underwater activities. Sea temperatures in June can reaching 25 C in several beaches of Kefalonia Island, making ideal bathing conditions for smaller children also.
The currents of the west coast are not so cold in June, so the best western beaches of the island, such as Petani beach, Myrtos beach or Fteri beach offer great experiences. It’s worth to know that the west coast sometimes is wavy, but these occasions the sea colours are magnificient!

July
In July, Kefalonia’s sea temperatures reach some of their highest levels of the year, with an average of 24-26°C (75-79°F). The waters are comfortably warm, making swimming, snorkeling, and diving enjoyable throughout the day. July is a peak month for tourism, with visitors flocking to the beaches to enjoy the sun and warm waters.

The relatively shallow coastal areas may even reach higher sea temperatures in Kefalonia, close to 26°C (79°F) – 27°C (81°F) creating ideal conditions for families and recreational swimmers. Marine activity is abundant due to the warm weather of June, with fish and other sea life easily visible, providing an excellent experience for snorkelers and divers alike.
The warmest sea temperatures in July in Kefalonia can be find usually on the southern side of the island, such as Xi beach, the beaches of Lassi, Lourdas beach, Agios Thomas beach, Avithos beach, Ammes beach, Ai Helis beach. The other beaches are also pleasant most of the time, so Myrtos beach, Antisamos beach, the beaches near Skala are also great for swimming and beach activities.

Don’t forget to book in advance the apartment or hotel in Kefalonia Island, because the accommodations are filled in the summer months.
The hotels and apartments in Kefalonia you can find by clicking here!
August
August is the hottest month in Kefalonia, both in terms of air and sea temperatures. The sea typically ranges from 25-27°C (77-81°F), with some sheltered bays reaching 28°C (81°F) in shallow areas. These warm waters of August are perfect for all-day swimming and attract large crowds to the beaches. The high temperatures provide comfortable conditions for water sports, including paddleboarding, jet skiing, and of course snorkeling.

In the weather of Kefalonia August is also an ideal time for underwater exploration, as the warmer waters support rich marine life, and visibility is often excellent due to minimal disturbance from winds or currents. The west coast, where Myrtos beach and Petani beach are located, can provide some waves, but these beaches have lifeguard service. When the waves getting big during the day, yellow and red flags indicate the higher risk.
Sea temperatures in August are very pleasant for everyone, making Kefalonia ideal holiday location in Greece (from the end of June till mid September this is also true).

September
In September the sea remains warm, averaging around 24-25°C (75-77°F), only slightly cooler than August. This sea temperature is still ideal for swimming and water activities, making September a favorite among those who prefer to avoid the peak tourist season while still enjoying warm, summer-like conditions.

The waters remain clear and calm, excellent for snorkeling and diving in Kefalonia Island. The sea temperature in September is also a time of increased marine biodiversity, with many fish species still highly active. The weather of September remains warm and inviting, and the sea temperature cools very gradually, making September a perfect month for beachgoers who enjoy a quieter experience.
The parasols and sunbeds are still standing on every beaches of Kefalonia, the bars and restaurants operates fully. The weather and sea temperatures of September in Kefalonia supporting outdoor and beach activites both well.

October
October brings a more noticeable change in sea temperature around Kefalonia, which cools to around 22-23°C (72-73°F). This range, however, is still relatively warm, and many swimmers find it comfortable, especially during the early part of the month. The cooler temperatures mean the beaches are quieter, though the sea remains welcoming for those who enjoy less crowded, tranquil conditions.

Many water activities, including snorkeling and kayaking, are still popular, with some marine species more active as they prepare for seasonal changes. By late October, however, the sea temperature may dip further, especially on cloudy or windy days, signaling the start of autumn.

November
In November, Kefalonia’s sea temperatures continue to cool, averaging around 19-20°C (66-68°F). This temperature is too cool for most of casual swimmers, it’s tolerable only for those accustomed to colder waters or wearing wetsuits. While fewer people swim in November, some outdoor enthusiasts, divers, and snorkelers still enjoy the sea, but most of the parasols and sunbeds are gone.

Marine life begins to slow down as the waters cool, with fish activity decreasing. November is a transitional month, with the sea reflecting the onset of cooler, less predictable weather, and by the end of the month, temperatures may dip further toward winter levels. The rains of November are cooling down the waters, and from this period the sea is less calm.
Summary of Kefalonian Sea Temperatures
- January: ~15°C (59°F) – Cold and not ideal for most swimmers.
- February: 14-15°C (57-59°F) – Cold, not suitable for swimming
- March: 15-16°C (59-61°F) – Slight warming trend, but sea temperatures are still very cool
- April: 16-17°C (61-63°F) – Beginning of the early swimming season, though still cool for most people
- May: 18-21°C (64-66°F) – Getting more comfortable for swimmers, sea temperatures can be suitable for shorter swims in shallow beaches
- June: 21-25°C (70-75°F) – Sea temperatures are ideal for all water activities, inviting temperatures for swimming and beach enjoyment
- July: 24-26°C (75-78°F) – Warm, ideal for all water activities, peak summer conditions for everyone, including children
- August: 25-26°C (77-81°F), up to 27°C (81°F) in some bays – Warmest month and warmest sea temperatures in Kefalonia Island, perfect for all-day swimming and snorkeling, vibrant marine life
- September: 24-25°C (75-77°F) – Still warm, great for swimming, quieter beaches, and ideal conditions for underwater exploration.
- October: 22-23°C (72-73°F) – Comfortable for some swimmers, but this period is beginning of cooler autumn conditions
- November: 19-20°C (66-68°F) – Cooler and less ideal for swimming, it is recommended just for experienced swimmers or divers with appropriate gear.