The best diving in Sumatra is Pulau Weh, a small island off the north west coast in Aceh province. Aceh province has been politically unstable for years and the December 2004 Asian tsunami also did devastating damage to the area. However the majority of dive sites escaped lightly with most of the damage being done from 0-10m deep with deeper areas of dive sites spared.
Pulau Weh is located off the north western tip of Sumatra and is actually Indonesia's furthest beach to the northwest. It's in the Indian Ocean and the diving season is the same as west coast Thailand and Malaysia with the high season running from November to April. There is accommodation and dive centers on Iboih where the jungle meets the beach or on Gapang Beach which has a nice house reef.
The marine life around Pulau Weh is superb on fringing reefs, walls and wrecks. There are over 20 dive sites around Pulau Weh, Pulau Rubiah and other surrounding islands. Many of the dive sites are suitable for all levels of diver but there are also some strong drift dives and some deep decompression dives that are only suitable for experienced divers.
Batee Tokong has very impressive marine life on it's steep slopes covered with encrusting sponge, zigzag clams and gorgonian sea fans. Pantee Aneuk Seuke (The Canyon) is a good dive spot to see manta rays. Napoleon wrasse can also be seen. Pantee Peunateung is a deep drop off to 70m where big schools of pelagic can be seen including barracuda and trevally. Currents can be strong here. Batee Gla is a also a good drift dive with strong currents. Rock formations create swimthroughs and archways framed by gorgonian sea fans and large schools of fish including snapper, fusilier, banner fish and surgeonfish. Pulau Seulako offers some good drift diving with the chance to see big fish. Arus Balee is a drift dive where the nickname given to the current hints at the strength of the flow. It is called the Acehnese Arus Balee, or Bastard Current! A rocky pinnacle in the passage between Pulau Seulako and Pulau Rubiah attracts bigger fish like barracuda, trevally and sharks. Other popular dive sites are Batee Meudoro Pinnacle, Shark Plateau and the Sophie Rickmers Wreck.