Answer:
Turtle has grown so much attached to the birds and trees that surround the pond.
Step-by-step explanation:
In the final stanza of the poem "The Turtle", the author Oliver Mary adds the word "swim" to present the idea that the turtle cannot see herself apart from the world because the turtle has grown so much attached to the birds and trees that surround the pond.
Just like how the turtle swims inside the water, the author connects the same essence with the birds that fly in the sky. Through this essence, the birds as well as the turtle are connected to one another and so she says that the turtle cannot seem to live apart from the rest of the world.