There is a scuba diving spot is only Okinawa but also south Izu Peninsula.
On the southern part of Izu peninsula close to Shimoda station, Mikomoto diving spot 15 minute away by boat from Yumigahama-kou 弓ヶ浜港 , is the most famous dive spot to watch hammerhead shark.
In additon, you would watch thounds of fishes as if you were in Shipadan in Borneo island. This means that there are so many migratory fishes in this area. The reason why is that there occur Kuroshio, means the black current. Due to the currents conditions, you will need to be capable of drift diving in the depth of the water 20m. Therefore, in order to dive Mikomoto, require at least PADI advanced open water certified with more than 50 dive logs history.
According to “MIKOMOTO HAMMERS”(http://www.mikomoto.com/english/), they require at least more than 30 dives experience.
Due to above reason, you need to check the following notes:
・You must not enter this area if your body condition is not good.
・When your body condition is not good, you should refrain dive this area.
・In some situations, you may consume much oxygen compared with normal spot.
However you do not need to fear a drift diving. Surely, under the usually with different situation, it is stressful for many people. In order to avoid strong current, the Diving guide is looking for a loose place of tide from the top of the ship entry. Most of time you stay middle depth water, but sometimes visible at the bottom of water, so you would feel relief.
[When to go]
Once in the range of 27 ℃ from 23 ℃, the appearance of hammerhead rate is thought to significantly up. The best season is from July to October, due to Kuroshio. Water clarity is 10m or more. Water temperature is Annual average around 19°C , but May to September average around 23°C.
The Shimoda is accessible departing from Tokyo easily. Perfect for a weekend getaway from Tokyo. “MIKOMOTOAMMERS”(http://www.mikomoto.com/english/) have pick-up service until the last train ( Shimoda Station arrival at 23:37 ) . The diving fee is 17,500 yen (2 dives per day per person for vister), and 24,500 yen(3 dives). If you would like to stay 1 night before diving, the accommodation fee is 2,500 yen (A room without meals), 3100 yen (With breakfast), and 3700 yen (With supper and breakfast).
For the detailed information, please refer to http://www.mikomoto.com/english/prices.html.