They are in the water up to their necks, using floats.

他们借助漂浮物在淹没到脖子的大水中行动。

They trekked nearly 200 miles in the cold, sometimes wading up to their necks in freezing water.

他们在寒冷中跋涉了近 200 英里，有时在冰冷的水中趟过脖子。