Bunaken Islands are surrounded by a fringing reef which is composed of a narrow reef shelf which then descends, sometimes vertically, to the external reef. Lagoons or patch reefs are rare.
More info about North Sulawesi reefs biology in:
All dives in Bunaken are done on the external reef, along the vertical walls. Most dives are drift dives. A mild current is almost always present (but seldom extremely strong): usually, the diving group follows the current along the reef slope and the diving boat picks you up at the exit. Currents are not dangerous as they run parallel to the reef gently pushing the divers into one direction. Perfect conditions for a beautiful drift dive!
In Manado Bay and Lembeh Strait, many dives are on sandy seabeds in calm water.
The main reason why diving this area is so attractive is the fact that you find exceptional biodiversity on these reefs, with the number of animal and plant species higher than in any other sea in the world. For more detailed information please refer to the pages “for the brain” and “biology”, and at the site www.edge-of-reef.com.
Potentially dangerous animals can be found, like the poisonous Laticauda colubrina seasnake, but these creatures are not aggressive at all. You just have to respect them and they will do you no harm.