"As the latter pass through the narrower and shallower Kampar watershed and meet the river flow, they will accelerate and bring about a big collision. The turbulence will produce large waves from four to five meters in height with a loud bang, similar to a tsunami wave."
But he pointed out that bono waves will continue to run along the watershed for about two hours, and gradually weaken with every turn of the river.
Bono waves are known to be destructive, because they cause erosion in the Kampar River and overflow onto land. They often flood houses with inundations of up to one meter in depth, and capsize fishing boats.
Yet this phenomenon is not a daily occurrence. Bono waves come about at high tide during a full moon, particularly as water levels on the Kampar River rise during the peak of the rainy season between October to December. they also occur from February to March.
The myth of the seven ghosts
According to an age-old Malay folktale called Sentadu Laut, bono waves are the embodiment of seven ghosts which often destroy canoes or ships crossing the Kampar River.
The tale described the seven ghosts as seven types of waves, starting from the largest wave in front, and followed by six waves that get successively smaller.
As objects of fear, the community elders would lead the inhabitants in holding a ceremony to placate the waves for their safety. On the other hand, bono waves are also a way for Malay warriors on the coast to test their courage and improve their fighting skills.
Bono waves remained Riau's best kept secret until Antony Colas, author of the surfing guidebook, World Stormrider Guide, visited the area in September 2010.