I have a pretty cool day job — reviewing pay TV for The Age and The Sydney Morning Herald. One of the best things about it is that I get to watch loads of great science programs. One of the things that drives me up the wall about it is that I have to watch so many bad science programs.

The thing that's got my goat at the moment is a fake documentary on Animal Planet called Mermaids: The Body Found. It has actors playing scientists talking about how they did an autopsy on some mermaid remains, and how the US government swooped and covered the whole thing up. There's grainy fake video of mermen being hauled up in fishing nets, the whole box and dice.

What annoyed me even more about this particular fake doco was the way it misrepresented evolution — not a great idea when nearly half of all Americans deny that evolution is real. 

The version that I saw doesn't even do viewers the courtesy of admitting that it's fake until the credits are about to roll. ''Ah,'' I hear you say ''but the story is obviously bulldust anyway''. Well, yeah, but Discovery (Animal Planet's parent network) puts bulldust to air with a straight face all the time. Whether it's demon hauntings, the chupacabra, Nostradamus's prophecies or James Cameron's ideas about the ''Lost Tomb of Jesus '' *cough*, Discovery is happy to create the impression that such things could be real — or at least that it's up to sceptics to prove that they aren't. (No, Discovery doesn't excel at identifying where the burden of proof lies).

What annoyed me even more about this particular fake doco was the way it misrepresented evolution — not a great idea when nearly half of all Americans deny that evolution is real. It starts off talking up the rather fringe "aquatic ape" notion of human evolution and ends up with some classic-looking CGI mermaids that make zero evolutionary sense. From the waist up they're slender modern humans (no insulating blubber? Brrr!), while from the waist down they're dolphins — and to top it all off they've got a dolphin-like sonar system inside their skulls. Over what period of time is all this supposed to have happened? A few tens of thousands of years? A few hundred thousand years?

The documentary makes much of the fact that whales evolved from terrestrial ancestors, but that took millions of years, not the kind of evolutionary eyeblink that Mermaids seems to be talking about.

It's not that there's anything wrong with a bit of speculative evolution, as long as you make it clear from the outset that you're making stuff up, and as long as you play by the rules of nature. The 2003 series The Future Is Wild (an Animal Planet co-production!) looked at what might evolve on Earth in the absence of humans in 5 million, 50 million and 300 million years' time — and it was brilliant.

And it's not as if Discovery and Animal Planet are on their own in pandering to an audience that's more interested in ghosts and aliens and biblical apocalypses than it is in real science or history. National Geographic has done some seriously cynical stuff about everything from UFOs to the supposed 2012 apocalypse, BBC Knowledge has touted ''new evidence'' that the Shroud of Turin is the real deal, and the History Channel always seems to be happy to have  conspiracy-theorist American preacher Tim LaHaye on to talk about his lurid rapture fantasies.

People love that sort of stuff, I get it. But it belongs on more tabloid channels that don't have any pretensions of scientific or historical credibility. And Discovery, Nat Geo and the rest make plenty of truly great television. They do themselves a disservice by making this sort of junk as well.

What do you think? Are sensational documentaries bad for science, or do they serve a purpose by attracting viewers who wouldn't watch more sober stuff? What are the worst science programs you've come across yourself?

Mermaids: The Body Found airs on Animal Planet on Sunday at 6.30pm

Around the science webs:

ERV looks at how viruses could help fight cancer.

Oceanographer's Choice looks at the effect of navy sonar on whales.

Ed Yong looks at how lunch breaks can affect judges' decisions.