Puerto Rico has been left reeling since Hurricane Maria smashed through the island on Wednesday. With 95 percent of the island’s cell sites down, residents are unable to contact first responders and family members. Over three million residents have been left without power or running water.In the island’s northwest, a major dam is now threatening to collapse. If the dam fails, it could create deadly flash flooding in surrounding towns. The National Weather Service warned residents to “stay away or be swept away”. About 70,000 people were ordered to evacuate amid the imminent threat.At least 13 people have been killed in Puerto Rico since the storm hit.