Java has hundreds of offshore islands around it's coast but most are little dived and still to be explored. Best months to dive are the dry season from April to October. Dive centres in Jakarta can arrange diving trips although getting around this crowded inland can be a chore.
A problem that heavily populated Java faces is environmental damage to offshore reefs from mainland pollution and sedimentation. Hopefully steps can be taken to protect the environment before the weight of the 20 million people causes irreparable damage.
Krakatoa (Krakatau in Indonesian) to the west of Java in the Sunda Strait is more famous for it's history of volcanic eruptions than it's diving. Underwater lava rocks create caverns and swim-throughs for divers to explore at several dive sites but coral coverage is poor. Moray eels can be found in the rock crevices. Large pelagics can be seen at some strong current dive sites. There are also several wrecks in the Sunda Strait including the HMAS Perth and USS Houston. Visibility ranges from 5-20m.
Ujung Kulon in the remote national park to the south west of Java has a similar volcanic underwater topography to Krakatoa. There's not much coral but plenty of fish life. Turtles, stingrays and barracuda can be seen at the dive sites in this area.
Palau Seribu means thousand islands and is the name to a group of many small islands off the north coast of Java. Access to the islands is easy by speedboat from the mainland and resorts on the islands offer diving daytrips. The fringing reefs around these islands are healthier than in other areas. Divers can see turtles, stingrays, moray eels and schools of reef fish here. There are also some wreck dives in this area.
Karimunjawa is a 27 island archipelago off the north coast of Java, a three hour ferry ride from the mainland. The area is divided into seperate conservation zones to help preserve the environment. Fringing reefs are healthy with clear water, colourful corals and good fish life.
Hawksbill turtles can be seen at Hawksbill Point on Menyawakan Island. Bumphead parrotfish can be seen at Torpedo Reef as can white tip reef sharks. Whale sharks are occasionally seen at Krakal Kecil and Krakal Besar.
There are also some wrecks around the islands including the Indonur, a large Dutch steamship that hit a reef in 1963 when her captain mistook a fire on a beach for the lights of Semarang. Large groupers can be seen on the wreck as well as moray eels, lionfish, scorpionfish and octopus.