At least 20 people died in the explosion of a wooden boat in southern Nigeria, a police spokesman said on Thursday. The vessel sank in Bayelsa State on Wednesday, but news of the incident in one of the region’s rivers was received much later due to the isolated location of the accident site. The number of victims could rise further as there were more than 60 passengers on board at the time of the accident. So far, only a few have been rescued alive. How the explosion occurred is not yet known. Boat accidents with high casualty rates are not uncommon in Nigeria. They are mainly caused by overcr…