why does the great gatsby reach out of the water?

Gatsby is actually reaching out to the green light at the end of Daisy's dock. He desperately wants to be with her. Gatsby is obsessive over this lady to say the least! Daisy is more or less an illusion. I always thought that Gatsby was in love with the idea of Daisy rather than Daisy herself. Still the light represents a haunting dream to Gatsby that he must fulfill.