Throughout "Fraggle Rock", humans have almost invariably been referred to by the Fraggles as "Silly Creatures". It's one of the most overlooked ingenious aspects of the whole series.
When we humans are the alien "other" to nonhuman point-of-view characters, you are almost guaranteed to see the rusty old "Humans Are Bastards" trope. The writers of "Fraggle Rock" are smart enough to not avoid it completely. But they put an unexpected fairer spin on it: humans aren't evil and we're certainly not intentionally mean, but we do some awfully confusing things sometimes. And sometimes we do things that would look downright stupid from the outside. We are, in a word, silly.
The Silly Creature we've been most concerned with in this series is... well, here's where things are going to get complicated, because where Canada and the United States had Doc, played by the irreplaceable Gerry Parkes, other markets around the world had a different human lead. The fascinating thing here is that nearly all versions of "Fraggle Rock" had an older gentleman as their equivalent character. You'd think our human emissary into the world of Fraggles, Doozers, and Gorgs would be a child for maximum audience-appeal points, and a less interesting series probably would have done that (there's a quick moment in "Uncle Matt's Discovery" where a little girl finds a Fraggle Hole that gives us a glimpse of that less interesting series). But there's "Fraggle Rock" for you, subverting expectations at every opportunity.
In any case, this is one of the very few episodes where the human world directly intrudes on Fraggle Rock. And your heart sinks at the revelation in the prologue that not only have humans found the "empty limestone caves" surrounding Doc's workshop and the Captain's Inn, it turns out that a few humans have already found an unsavory use for them: as a potential "safe" dumping ground for industrial waste.
I grew up in the early 90's. I've seen a lot of programs try to do a "save the environment" episode. An awful lot of them fail because they end up in way over their head; usually the issue ends up either too simplified or too overbearing. Jim Henson would go to this well quite a few times, and he'd usually do a better job than most. But I think this is his most powerful take on the issue, one of the best attempt at such an episode ever made by anyone really, and here's why: At this point in the series, we've spent so much more time in the Rock than in the human world that it feels more like home than the human world does. We've spent three and a half seasons with the Fraggles; that's basically like going to college with somebody. So learning that somebody intends to dump poisonous industrial byproducts into the caverns of Fraggle Rock does not strike us viewers as a sad -- but faraway! :D -- tragedy (to borrow a phrase from another series). No, it is nothing less than an incredible violation of our own home and beloved friends. It's unthinkable.
And it gets worse. Because here's the other remarkable aspect of his episode: who is this human who is threatening our home and our friends? Who is this person who could, just by agreeing to the dumping, doom the Fraggles to extinction and the entire Fraggle Rock ecosystem to complete annihilation without even realizing it? It isn't some dedicated "eco-villain" a la "Captain Planet" who evidently just thrives on hurting living things for the hell of it. It's not a random character who is going to show up for only this episode, naively causes harm, learns to not do that, and promises never to pollute again and therefore gets to be an honorary Planeteer (yeah, this isn't the most original observation, but "Captain Planet" was not very good). And it's not even a big, faceless scary corporation. No, this episode doesn't go the easy route. The person who could inadvertently kill all these wonderful characters we've grown to love over the years is Doc. Yes, dear old kindly Doc, the nicest human character of all. Doc who we know and love. Doc, who we know would never in a million years do anything that would hurt another living thng, and certainly wouldn't even think of harming Fraggle Rock if he knew about it. Holy sh*t, this episode; is it trying to kill me over here? I need a beer and a good long stare at the wall, guys.
And so help me, it gets WORSE! Because Boober, the only resident of the Rock who hasn't been poisoned, has tracked the source of the pollution to Outer Space. And in a scene that is less "sad" and more "brace yourselves, audience, cause now we are just going to tear out your guts and stomp all over them", he kneels down at the entrance to Doc's workshop and pleads with the Silly Creatures to stop hurting his friends. The thing is, he doesn't know that Doc and Sprocket have stepped out for a while, and the workshop is totally empty... except for us Silly Creatures in the audience... Oh, God...
The episode ends with the residents of Fraggle Rock well again, singing and merrymaking as usual thanks to Doc calling off the dumping project... and with Doc seriously wondering for the first time at those mysterious caverns under his home, thanks to the stack of postcards addressed to one Gobo Fraggle that Boober had left at the entrance to the tunnel to Outer Space. The more I think about it, the more I think this may be the single most profound episode of the entire series.