Ehime National Park | Scuba diving trip to the sea. Ainan Town - Nishikai Sightseeing Boat [2/4]

Located at the southern tip of Ehime Prefecture, Ainan Town is home to an ocean with a unique environment, even on a global scale. It is also a famous scuba diving spot in Japan. The abundance of different environments in the same area makes it unique for the overwhelming number and variety of fish.

Written by

Ainan Town Hall

Located in the southernmost part of Shikoku's Ehime Prefecture, Ainan Town is an area blessed with a rich natural environment, including the abundant sea and mountains represented by the Ashizuri-Uwakai National Park. The climate is warm throughout the year, and you can see coral and tropical fish.

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Table of Contents
Ainan Town, a town surrounded by ria coastlines | Many diving spots
Simple introduction to underwater scenery
Diving Style | Schedule & Facilities Introduction Saikai Sightseeing Cruise
Recommended season, seasonal winds and water temperature
Nearby hotel | About 10 minutes by car to the shop
More Articles and Outside Resources ｜Southern tip of Ehime, Ainan Town, Nishikai Sightseeing Boat

Ainan Town, a town surrounded by ria coastlines | Many diving spots

Ainan Town, located at the southern tip of Ehime, is surrounded by a unique coastline created by a ria coastline. Due to the presence of uninhabited islands nearby, different environments are scattered across a small area. There are over 30 diving spots. A multi-day diving plan is recommended. The best time to visit is between July and the end of October.

Simple introduction to underwater scenery

Yokoshima, where soft and hard corals gather

Yokoshima, designated as a special protected area of the national park, has five diving spots. The three spots we often take people to are Yokoshima No. 2 Site, Yokoshima Fault, and Koyokoshima. Each spot has its own characteristics, so we will introduce the underwater conditions.

Yokoshima Site No. 2

Yokoshima No. 2 is a point where a ridge stretches out with a difference in elevation. The bottom at the tip is 35m deep, and the top of the ridge is about 10m. This is a terrain that attracts fish, so if you're lucky you might be surrounded by schools of grunts, silver-ringed herring, and amberjack.

Yokoshima Site No. 2

What all the points on Yokoshima have in common is the presence of colonies of hard and soft corals in shallow waters.

Yokoshima Fault

The Yokoshima Fault is a very shallow area, with a maximum depth of 14m and an average depth of 8m. A single rock stretches from north to south, but above it is a magnificent, unbroken colony of coral.

Koyokoshima Island

Like the other spots we've introduced so far, coral colonies grow in the shallow areas of Koyokojima, but if you go down to the sandy area below, you'll often come across large schools of fish. Sometimes schools of thousands of grunts and other fish will fall from above all at once, making this a spot where you can target both coral and migratory fish.

After the safety stop, we explore the cave before returning to the boat. It is a fun spot where the environment changes constantly during the dive, with corals, fish, and topography.

Diving Style | Schedule & Facilities Introduction Saikai Sightseeing Cruise

schedule

We dive three times a day.

8:30 meet up
9:00 Departure
9:30-10:30 1st dive
10:30(you can choose this time, when you wanna only 2dive/day)
11:00 Departure
11:30-12:30 2nd dive
12:50-13:30 Lunch Bento
13:45 Departure

2Dive 14,000 Yen
3Dive 18,000 Yen
Full rental 5000Yen + Divecomputer 1500Yen

Locations, Facilities, and Ships

Name of the shop: Nishikai Sightseeing Boat Address: 1599 Funakoshi, Ainan-cho, Minamiuwa-gun, Ehime Prefecture, 798-4205
Google Maps is here▽
https://maps.app.goo.gl/wuLyy78Vxgab5AWy9
Official website/Fun Diving is here▽ (Japanese)
https://nishiumi.info/scuba-diving-fun.php

The parking lot is large and can accommodate 150 cars, with a view of the ocean.
Please come to the reception desk in the building in the photo and tell them you want to go diving before the meeting time. We will guide you there.

Diving Style | Boat & Anchoring

We occasionally do drift diving, but the basics are boat and anchoring diving. We have created many courses with varying terrain, and we guide everyone on circular courses.

We also have SSI (Scuba Schools International) instructor trainers on staff, so we have the advantage of being able to hold all courses, including professional rank instructor courses. We will guide everyone with safety as our number one priority.

▽ Reservations can be made here: Saikai Sightseeing Cruise Official Website (external site, Japanese)
https://nishiumi.info/scuba-diving-fun-reservation.html
▽Seikai Tourist Boat Official Website Fun Diving Explanation (external site, Japanese)
https://nishiumi.info/scuba-diving-fun.php

Recommended season, seasonal winds and water temperature

Recommended time: Mid-June to late October

In the summer, the sea is as calm as a lake, as shown in the photo above. We recommend visiting from mid-June to the end of October.

You can dive in winter, but the seasonal winds are often strong from November to the end of May, so the seas tend to be rough (January and February are the peak months). When the sea conditions are bad, we often cannot go to Yokoshima, which is our main diving point.

During the winter, there are often 6-7 stormy days out of every 10 days.

*A detailed wind forecast will be announced two days before your reservation. Based on that forecast, we will contact you if there are any problems with the sea conditions.

Water temperature: 16°C to 28°C (minimum water temperature is in February, maximum water temperature is at the end of August)

The maximum water temperature in this area is 28°C. The water is warmest from the end of August to early September. From mid-June to the end of October, you can comfortably dive in a 5m wetsuit. (On October 22, 2025, the water temperature was 26°C.)

The lowest water temperature is 16°C around February. As the outside temperature also drops at the same time, we recommend wearing a dry suit from November to the end of May. Dry suits are limited in number for rental, so please contact us in advance if you require one. A dry suit special is required for rental.

Nearby hotel | About 10 minutes by car to the shop

Hotel AZ opened in Ainan Town in 2025. It has over 140 rooms. It's close by, so I recommend it.

▽HOTEL AZ Google Map
https://maps.app.goo.gl/FrTmWGjWMC7sayCZA

More Articles and Outside Resources ｜Southern tip of Ehime, Ainan Town, Nishikai Sightseeing Boat

▽Ehime National Park Nishikai Sightseeing Cruise [1/4] | Shop Introduction

Ehime National Park | Marine Activities. Ainan Town - Nishikai Sightseeing Boat [1/4]

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▽Ehime National Park Nishikai Sightseeing Cruise [2/4] | Scuba Diving

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▽Ehime National Park Nishikai Sightseeing Cruise [3/4] | Environmental Conservation & Coral Conservation

Ehime National Parks | Our Environmental Conservation & Coral Conservation & Town: Ainan Town and the Nishikai Sightseeing Boat [3/4]

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▽Ehime National Park Nishikai Sightseeing Boat [4/4] | Ainan Town's Marine Environment

Ehime National Parks | Special Protection Areas, Marine Characteristics, Environmental Conditions. Ainan Town, Nishikai Sightseeing Boat [4/4]

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▽Ehime National Park Nishikai Sightseeing Cruise, official website here (Japanese, external site)
https://nishiumi.info/

Written by

Ainan Town Hall

Ehime

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