Answer:
Autumn.
Step-by-step explanation:
The poem "The Wild Swans at Coole" by William Butler Yeats talks of the poet's memories about the wild swans he had seen at the lake. He remembers how the swans used to paddle in the water or fly in the air. He also remembers just how lovely it was to see them and that it's been nineteen years since he first came here.
Now that the years have passed, he also noticed that life changes but not for the swans. They still swam in the lake and enjoy the lake. The poet also reflects on the beauty of these swans, fifty-nine swans to be precise. The season of the actual setting of the poem can be known for the poet himself mentioned it in the poem, "The trees are in their autumn beauty" or "October twilight". These words/ phrases prove that the poem was written during the autumn season.