Pack ice around Iceland was becoming a threat to navigation.
冰岛周围的浮冰一度成为船舶航行的威胁。
《柯林斯英汉双解大词典》
2
Navigation was confined to shallow vessels, tricky enough even in the few summer months when the river was free of ice.
航行船只局限于小船，即使在短短夏季数月的无冰期，通行起来也足够困难。
3
But even if the ice melts as fast as shippers hope (and scientists fear), navigation is likely to demand strengthened hulls, higher insurance and extra training for crews, all adding to the costs.