He is forced to head out into deeper water. 它必须进入更深的水域

227. In these new surroundings, he is a surprisingly adept swimmer.
     在这个新环境里, 北极熊变成了一个身怀绝技的游泳高手
228. 0nce an extremely rare sight, polar bears have recently been seen over 60 miles from the shore.
     曾经有人在离海岸60英里处发现了北极熊 这种事情是极难碰到的
229. There is now no turning back for this bear.
     现在已经没有回头路了
230. He is forced to head out into deeper water.
     它必须进入更深的水域
231. His giant front paws help him to fight the ocean currents.
     它那巨大的前爪有力地拨动着海水
232. He seems at home in the sea,
     在海里它似乎是那样地悠游自在
233. but he cannot swim indefinitely.
     但是它不能永远游在水里

来自《行星地球 第一季 第六集 Planet Earth S01E06 冰雪世界》第 230 行