Kerama Blue Waters: A Diver's Sanctuary

Aka Island (Akajima) sits inside the Kerama Islands National Park, a cluster of coral-fringed islets about 30 kilometers west of Naha. Divers here chase what local shops nickname "Kerama Blue," a startling gradient of turquoise-to-cobalt water caused by unusually low plankton density and a seafloor of fine white coral sand that reflects light back up through the water column. Visibility regularly exceeds 25 meters on calm days, rivaling or beating better-known Okinawan dive destinations while drawing a fraction of the crowds.

What sets Aka apart from its sister islands Zamami and Tokashiki is its shape: the island wraps around a deep, current-sheltered bay, so boat rides to dive sites rarely exceed ten minutes even in choppy weather. That short transit window makes Aka a favorite for dive operators running three-tank days, since surface intervals can be spent back at the pier rather than bobbing offshore. The resident population is small (under 300 people), and the island has resisted large-scale resort development, so the coastline still looks much as it did decades ago — a deliberate contrast to the built-up dive piers you find on Ishigaki or mainland Okinawa.

Green sea turtles are effectively year-round residents around Aka's western reefs, feeding on seagrass beds close enough to shore that many arrive by snorkel rather than scuba. From January through March the same waters double as a humpback whale nursery; boats heading to dive sites during those months often cut engines mid-transit when a whale surfaces, turning the ride itself into a wildlife encounter before anyone has even geared up.

Beneath the Surface: Dive Sites and Underwater Terrain

The reef structure around Aka is a mix of fringing coral shelves, sand channels, and a scattering of pinnacle formations that rise from 18–25 meters to within a few meters of the surface — ideal for multi-level dive profiles. Nakanohama Point, on the island's protected east side, is the standard checkout and training site: a gently sloping coral garden capped at 12 meters, with staghorn and table coral providing cover for clownfish, mantis shrimp, and juvenile batfish. It's shallow enough that visibility problems from surface chop rarely reach the bottom.

For more experienced divers, the channel between Aka and neighboring Geruma Island funnels tidal current through a series of coral bommies known locally as the "Geruma Alley." Current here can run strong on spring tides, turning the dive into a drift along a wall studded with soft coral and gorgonian fans, with a reasonable chance of spotting eagle rays cruising the blue water off the reef edge. Because the current is tide-dependent, shops schedule this site around slack water windows rather than fixed daily slots, so exact timing shifts with the lunar calendar.

On the southwest tip, a series of granite boulders — a rarity amid Okinawa's otherwise coral-dominated seascape — creates swim-throughs and overhangs locally called the "Megane" (eyeglasses) formation for the two circular tunnels divers pass through in sequence. Sand patches below the boulders host garden eels and occasional resting nurse sharks. Because this site sits slightly more exposed to open ocean swell, boats generally skip it when wind exceeds 15 knots, so it's worth asking your shop whether "the Megane run" is on the day's plan rather than assuming it's a default stop.

Depth ranges across Aka's sites span roughly 5 to 30 meters, making it workable for open-water certified divers on their first ocean dives as well as advanced divers looking for drift and swim-through routes. Water temperature swings from around 21°C in February to 29°C in August, so a 3mm wetsuit covers most of the diving season, with a 5mm or hooded vest recommended for winter whale-season trips.

Season, Access, and Logistics

Aka Island has no airport, and that's part of its appeal — it filters out day-trip crowds that overwhelm more accessible reefs. The standard route starts at Tomari Port in Naha, where a high-speed ferry (around 70 minutes) or a slower car ferry (about 2 hours) crosses to Zamami Port. From there, a short local ferry or water taxi (roughly 15 minutes) connects to Aka's own pier. Most dive shops on Aka will arrange this final connection if you book a multi-day package, since ferry schedules to Aka itself are limited to a handful of daily departures and sell out during Golden Week and Obon.

The dive season runs essentially year-round, but conditions shift meaningfully by month. April through June offers the calmest seas and building water temperatures before the rainy season's occasional squalls. July through September is peak warmth and peak visibility, but also typhoon season — it's common for one or two dive days per trip to be cancelled or rescheduled during this window, so travelers should avoid booking single-day itineraries in late summer. October and November bring drier air and still-comfortable water. December through March is whale season, with cooler water rewarding those willing to wear a thicker suit for the chance to hear humpback song underwater between dive sites.

Because Aka is small, most dive shops require advance reservation rather than walk-up bookings, and many close entirely for a few weeks in January for boat maintenance ahead of whale season. Nitrox fills are available at the two main operators on the island but should be requested at time of booking rather than assumed. Cash remains preferred for gear rental and fuel surcharges; the island's only ATM is inside the village store near the port and occasionally runs out of cash on holiday weekends, so carrying yen from Naha is the safer bet.

Island Life: Where to Sleep, Eat, and Prep Your Gear

Accommodation on Aka is almost entirely small, family-run minshuku (guesthouses) rather than hotel chains, many of which are owned by the same families operating the dive boats — booking lodging and diving together often unlocks a modest package discount that isn't advertised online and has to be asked for directly. Rooms are simple, tatami-floored, and typically include two home-cooked meals a day featuring the island's namesake specialty, umi-budo (sea grapes), alongside grilled reef fish and Okinawan soba. There are no convenience stores on the island, so anyone with dietary restrictions should mention them at booking rather than expecting alternatives on arrival.

Rinse facilities for dive gear are available at most guesthouses and at the pier itself, but freshwater is a limited resource trucked in from Naha, so long gear-rinsing sessions are gently discouraged during dry summer months when the island occasionally faces water restrictions. Pack reef-safe sunscreen; several shops on Aka have voluntarily banned oxybenzone-based products to protect the coral that makes the diving worthwhile in the first place, and will ask you to switch before boarding if they notice a banned brand.

Evenings on Aka are quiet by design — no nightlife strip, no izakaya row — but the payoff is a night sky largely free of light pollution, and several guesthouses will lend stargazing mats on clear nights. For divers wanting to extend the trip, Nishibama Beach on the island's north side is consistently ranked among Japan's best beaches and makes an easy no-tank day between dive sessions, with turtle sightings possible even from the shoreline. Because everything on Aka closes early and options are limited, the most useful practical tip is logistical: confirm your return ferry time before your last dive day, since missing the last Zamami-to-Naha connection means an unplanned extra night on an island with very few spare beds.