The Dolphin Dilemma

Decades ago, researcher John Lilly claimed that dolphins understood human speech, and suggested that science find a way to create a form of communication between the planet's two most intelligent species.
But what if no translation were needed, and dolphins have been able to speak to us all along?
Maybe these brilliant creatures simply haven't felt the need to communicate with humans, since doing so surely would cause a nuisance within the happy, peaceful society they've enjoyed for 30 million years.