A couple of months ago, a killer started mobilising off the South Australian shore — one that would wipe out marine life, make surfers feel sick, and smother picturesque beaches in thick foam.

The culprit? A bloom of tiny organisms called microalgae. We can't see them with the naked eye, but in big enough numbers, they can devastate ecosystems.

So what made the South Australian algal bloom so lethal, and can anything be done about blooms like it?