The reefs around Menjangan Island, off the northwestern tip of Bali, were once among the best dive sites around Bali, if not Indonesia. But in the late 1990s the reefs were beset by catastrophe. First, in 1997, there was a population explosion of coral eating Crown-of-Thorns sea stars. A year later what coral remained was bleached by abnormally warm waters bought on by El Niño. However, the damage was mostly limited to the shallow reefs, and the deeper walls still remain healthy.
The northwest of Bali is the least populated area of the island, and a large portion of it is reserved as a national park. Most of the dive sites are along the northern coast, from Menjangan Island eastward, but there are some dive sites around Gilimanuk, the city that is the 'gateway' between Bali and Java.
There are only a couple of resorts close to the center of the area, and there are, apparently, no dive operators here either. More accommodation options and several dive operators can be found in nearby Pemuteran.