Futo Visibility Analysis — 3,400 Days of East Izu Diving Data

Just 2km from IOP, yet 2.3m lower in visibility — Futo's data reveals why geography matters more than proximity. 3,493 days of East Izu diving analyzed.

Our site has collected visibility data from the Dolphin Wave blog, accumulating 3,493 days of observations. This exceeds even the dataset for Izu Oceanic Park (3,240 records), making it one of the largest datasets among all sites we analyze. In this article, we examine Futo's visibility patterns from multiple angles, including direct comparisons with its neighbor IOP.

Monthly Visibility Patterns: The Classic Izu Winter-Clear Cycle

Futo exhibits the characteristic "winter-clear, spring-murky" pattern common to East Izu dive sites. The highest visibility occurs from December through February, when conditions consistently exceed the annual average. This winter clarity is driven by two primary oceanographic factors: the influx of clear, nutrient-poor Kuroshio Current water along the east Izu coast, and the suppression of phytoplankton activity as water temperatures drop.

The lowest visibility occurs from March through May, a period known in Japanese diving culture as "haru-nigori" (spring turbidity). As water temperatures rise and daylight hours increase, phytoplankton undergo explosive blooms, turning the water greenish and reducing visibility significantly. However, this period coincides with peak macro life activity: nudibranchs and the beloved lumpfish (dango-uo) juveniles appear in abundance, making spring a paradise for macro photographers.

From summer through autumn, visibility gradually recovers. After typhoons, Kuroshio-derived water can flush the area and produce spectacular overnight improvements. October and November represent the "golden season" when water temperatures remain comfortably warm while visibility climbs back toward winter levels.

Comparison with Neighboring IOP: Different Conditions Just 2 km Apart

Futo and Izu Oceanic Park are separated by only about 2 kilometers, yet differences in entry point orientation and topography mean that conditions can vary between the two sites on the same day. IOP's main entry is from a rocky shore facing the open ocean, where tidal flow is strong and offshore water penetrates directly. Futo's Yokobama, by contrast, is a sheltered cove where bay water and open-ocean water mix.

As a result, there are days when IOP is closed due to rough conditions while Futo remains diveable, and vice versa. When planning a dive trip to East Izu, keeping both sites as options allows for flexible decision-making based on the day's sea conditions. While average visibility values are not dramatically different between the two sites, Futo's Yokobama often has the advantage in terms of entry comfort and safety.

In terms of data volume, Futo (3,493 records) surpasses IOP (3,240 records), making it the most statistically reliable data source for understanding East Izu visibility trends. The sustained, long-term observation reflects the active diving community operating out of Futo.

Yearly Trends: Long-Term Visibility Changes

The yearly data shows no long-term deterioration in visibility at Futo. Year-to-year fluctuations correlate with the path of the Kuroshio Current: years when the Kuroshio runs close to the Izu Peninsula tend to produce higher average visibility, while years of large meander (dai-dakoh) see somewhat lower values. The ongoing large meander that began in 2017 may account for some suppressed years, but the overall environment remains stable.

Comparing Futo's yearly trends with IOP reveals a loose positive relationship, as expected for neighboring sites under the same large-scale oceanographic forcing. However, individual years sometimes diverge, underscoring how local bathymetry and exposure differences modulate the shared Kuroshio signal.

AI Prediction Accuracy: What AI Accuracy 42% Means

Our prediction model achieves an AI accuracy of 42% (general AI) for Futo. The site-specific AI scored slightly lower at 41%, so the general AI was adopted. An AI accuracy of 42% means the model explains approximately 42% of the variance in visibility.

What makes this particularly interesting is the stark contrast with neighboring IOP, which achieves an AI accuracy of 82% — among the highest of all sites. Futo's score is roughly half of IOP's despite being just 2 km away. This discrepancy is primarily attributed to Yokobama's cove-like topography responding in complex ways to subtle wind and tidal changes, localized sand resuspension in the sandy areas, and differences in data recording methodology.

Nevertheless, the model captures seasonal patterns and weather relationships well enough to serve as a useful planning reference. Winter stability and post-rain visibility drops, in particular, are predicted with relatively good accuracy.

Practical Diving Advice

Yokobama: A Gentle Entry for All Levels

Yokobama is Futo's defining feature. Unlike IOP's rocky giant-stride entry, Yokobama offers a gradual sandy slope where divers can walk in at their own pace. This makes it an ideal site for beginners, refresher divers, and anyone carrying heavy camera equipment. The shallows are rich with soft corals and nudibranchs, offering plenty of interest without needing to go deep.

A Macro Photography Haven

Futo has earned a reputation as one of Izu's premier macro photography destinations. The sandy areas host gobies, frogfish, and various crustaceans, while the rocky reef zones are rich with nudibranchs, shrimp, and juvenile fish. Octopus sightings are also notably frequent. Even on days with reduced visibility, macro photography remains thoroughly enjoyable.

Best Times to Visit by Objective

• Maximum visibility: December through February. Winter brings the clearest water. Drysuit required.
• Best balance: October through November. Warm water with improving visibility. Pelagic fish season.
• Macro photography: March through May. Spring bloom reduces visibility, but subjects are at their peak. Lumpfish season.
• Beginners: July through September. Yokobama's gentle entry combined with warm water makes this the most comfortable period.

Choosing Between Futo and IOP

Southwest winds tend to favor Futo, while northeast winds often leave IOP in calmer conditions. The two sites are only about a five-minute drive apart, so checking conditions on the day and choosing accordingly is the wisest approach. Consulting with local dive shops in advance will help you get the best recommendation.