Australian. I've seen this circle the internet many times, but I've never seen one in the wild at any beach or river outlet.
In general, Australian's culture is to use rubbish bins and keep things tidy.
Sidepoint: I am not sure if it is something only Australians do, but whenever something about Australia comes up, there will be an Australian there bemoaning how badly we do things. Yes, there is always room for improvement, but Australia is so far ahead of most countries in just about any measure that you choose, that one has to wonder where this sentiment stems from.
And there are a number of areas where we certainly aren't ahead either.
Whether the discussion be about environment, politics, innovation, corruption, you name it, some Australian will start moaning about how badly we do X.
I.e., there's no "Australia" program to install these nets, as far as I know.