A couple are walking through the 'gulping' mud alongside a lake in winter. They are 'silent and apart' and the reader feels as if the previous 'two days of rain' might have coincided with an argument between the pair. They appear distant.
When the swans arrive, the pair stop to watch the birds and their 'show of tipping in unison’. The birds are compared to icebergs and 'boats righting in rough weather'. They might be seen as reflecting the relationship between the couple, who are also on the verge of 'righting' their relationship after a difficult patch.
The speaker's partner comments that the birds 'mate for life' and this observation seems to remind the pair that they have done the same. Where the first half of the poem refers to storms and darkness, we now have a mention of 'light', implying a positive turn for the relationship.
By the end, their hands have ‘swum the distance between’ them and folded ‘like a pair of wings’, implying that their differences are now reconciled.