This poem seems very sad to me. It sounds as if the author is watching an animal that was just killed, by a boat or something in the lake, by people. He doesn't want to believe it at first, but he watches as her hungry offspring come, not knowing now that their mother is dead and we know that they will die too.
It seems to me that there is anger in this poem, too. The author is standing between the road and the lake as cars go by
"not moved by the madness
of three hundred cars in ten minutes
here where the woods might have been."
He says he is "here where the woods might have been" I think with some sort of resentment towards mankind. He clutches a stick in his hand as if he is angry at the people driving by for killing the woodchuck.