Home to some of the strangest (and most venomous) creatures in the ocean, the GBR is a poster child of what we stand to lose as the oceans warm. I had always wanted to see it for myself.

So one morning, on an ocean as flat and blue as a swimming pool, empty of other boats all the way to the cloud-strewn horizon, I hold a mask and regulator to my face and step into the water.

Underneath, huge mounds of coral rise 30 feet from the seafloor almost to the surface. I am surprised to find that these seamounts — called “bommies” in Aussie — are veritable catalogue advertisements of reef health and diversity. I see all kinds of Acropora — big, branching thickets of elkhorn, wide terraces of tabletop coral — all colored a healthy deep orange or yellow. Pocillopora sit on the tops of lower mounts like frilly heads of lettuce. I see enormous brain corals and tiny, fine-fingered soft corals that swayed in the current.

All around these pillars and buttresses, life swarms and flashes like static electricity: angelfish, damselfish, clownfish, a massive school of yellow-finned jacks winding between two bommies. There are skates bearing blue spots the size of silver dollars and parrotfish in all the colors of an 80s aerobics instructor’s leotard. Electric-blue sea stars stand out like asterisks on the sand, where giant clams flick their purple lips as I swim over.

If there is trouble on the Great Barrier Reef — and, by all accounts, there is — I can’t see a sign of it from behind my mask. In all its wild wholeness, this little patch of Edenic reef seems to stand both for what has been lost everywhere else, and what we stand to save.

But as I haul myself back out of the water — suddenly transformed back into a clumsy two-legged creature wearing sixty pounds of dive equipment and a fogged mask in front of my face — I feel both smaller and bigger than before. No matter how much I wanted to believe it while I was underwater, I knew that the idea of a pristine reef is an illusion. There are no virgin reefs to “preserve.” Any reef, any ecosystem, no matter how lovely, is in the process of being affected by the 7 billion (and counting) people of the world.

But that’s the way it’s always been. The reef is always changing: It is fed by currents and smashed by storms, and subject to the whims of the animals moving in waves over it. Flux is a fact of nature, and human are now a part of that. If we want to start setting right some of the balances we’ve upset, coral reefs are as good a symbol as any of where our real work begins — at the intersection between the world and ourselves.

This piece originally appeared in Grist.