About trying to rescue someone you care for deeply, possibly a former lover, from sinking deeper and deeper into depression.
The sea/depression analogy here is apt, because like depression, the deeper you fall and the longer you are underwater, the more dangerous it becomes. The singer is trying to keep someone from being so swept away by their sadness that she can't reach him/her anymore.
About trying to rescue someone you care for deeply, possibly a former lover, from sinking deeper and deeper into depression.
The sea/depression analogy here is apt, because like depression, the deeper you fall and the longer you are underwater, the more dangerous it becomes. The singer is trying to keep someone from being so swept away by their sadness that she can't reach him/her anymore.