One of the issues Hayao Miyazaki addresses in Ponyo is the vast amounts of in our oceans, lakes and streams. In this early scene, Ponyo becomes ensnared in a garbage patch, and eventually becomes caught in a glass bottle. But this is not something from the director's imagination; this is the shocking reality of the state of our world.
With the prosperity of the 1950s, America adopted a disposable society, a culture of ease and convenience. This was the mark of progress after so many years of depression and war. But this attitude created a throwaway society, where endless mountains of garbage are piled up, shoved out the door, and forgotten. Out of sight, out of mind.
The worst culprit by far are the plastics. Plastics will one day be seen as one of mankind's greatest failures. In the pursuit of instant gratification and laziness, we have created a substance which is completely indestructable. The polymers of these plastics will never fully break down, never bio-degrade over time. Centuries from now, this growing piles of plastic will still be here, many of them virtually untouched from today.
The worst revelation of all? Most plastics cannot be recycled. Repeat that to yourself. Most plastics cannot be recycled. Nearly every piece of plastic ever made still exists in the world today. And we are creating mountains of plastics at a staggering rate.
The devestation of the environment is a common theme in the works of Hayao Miyazaki and Isao Takahata. All they needed for inspiration was to look outside their windows, and take a look into the oceans. These movies are not simply passive entertainment designed to numb your brains. These are dire warnings for the future. In Ponyo, Miyazaki's rage and rebellion against this modern civilization boils over into apocalyptic devestation. For him, this is no warning; we have moved far beyond that. This is revenge.
You can read about the Plastic Oceans with any Google search. Begin here, then go here, here, here, here, here, and here.