Greek boy who fell in love with his reflection

Narcissus was the son of the river god, Cephisesus. In Greek Mythology Narcissus was a hunter, who was a beautiful young man. He saw his reflection in a pool of water, and became entranced by it. He refused to leave or disturb the water because of the fear of losing his reflection. Narcissus ended up dying of thirst and would later appear as a narcissus flower.

What poem? what author?