It has been estimated that container ships lose between 2,000[91] and 10,000 containers at sea each year,[92] costing $370 million.[93] A more recent survey for the six years 2008 through 2013 estimates average losses of individual containers overboard at 546 per year, and average total losses including catastrophic events such as vessel sinkings or groundings at 1,679 per year[94] Most go overboard on the open sea during storms but there are some examples of whole ships being lost with their cargo.[95] When containers are dropped, they immediately become an environmental threat – termed "marine debris".[96] Once in the ocean, they fill with water and sink if the contents cannot hold air.