I have a confession to make: For nine years I made a TV show, River Monsters, that left some people believing that everywhere you go, there are fish that can bite pieces out of you or pull you under. But its not quite like that.

The fish are real enoughfrom dog-sized super-piranhas in the Congo to 300-pound river stingrays in South America, and armor-plated alligator gar in the U.S.and youd be well advised not to get too close to most of them. But the thing is, theyre really hard to find. So the chances of ever being in the wrong place at the wrong time are reassuringly small.

But (anglers would say) surely thats the whole thing about big fish: Theyre a lot smarter than small fish, and there arent so many of them. Thats true, but they havent always been as scarce as they are now. Fish have been in our rivers for 300 million years. This decline has happened in just a few human generationsthe last 100 years.

Unlike the state of our oceans, which is well documented, this story isnt widely known. Its something that has slowly revealed itself to me over 35 years, during my travels to far-flung rivers. Partly its from historical records, but mostly its oral history, which nobody has ever collated or written down. Its a vast database, but it exists only in the memory of the old fishermen, who are dying as we speak.

What Ive been doing since 1982, without realizing it until very recently, is taking blood samples. And the results demand investigation.
Jeremy Wade

So why am I telling you this now? Because it has a significance that goes way beyond making my life harder when Im on a film shoot.

Long before I worked in TV I was a biology teacher, and in science-speak most of the fish that I go after are apex predatorsthey sit at the top of the food pyramid. That makes them really good indicators of the health of the whole river. If the apex predator is there, you can normally assume that the rest of the pyramid is there toothe middle-sized fish that they eat, the small fish that they eat, and all the bugs and plankton that they eat. But if the apex predator is not there, it suggests that something is wrong.

Take a minute for a quick thought experiment. Imagine someone discovering that they have an abnormally low count of white blood cells (the apex predators of the bloodstream). What do they do? They go for more tests, as a matter of urgency. They want to find out how serious this is, and whats the prognosis. Most importantly, they want to know what can be done about it. What they dont do is ignore it.

Now consider what is often said about our rivers: that they are our planets arteries. If thats the case, then what Ive been doing since 1982, without realizing it until very recently, is taking blood samples. And the results demand investigation.

The obviousand simpleexplanation for the decline of these top predators is overfishing. But it could be a symptom of something more serious. Thats the real worry. And its important we look into this because we are water-based life forms too. Water doesnt just cycle from rivers to oceans to clouds to rain and back to rivers againit flows through every one of us, through every cell in our bodies. So we all have a vested interest in the state of our planets water.

This was the genesis of Mighty Rivers, and it was an insight that meant putting everything else on hold. But where to begin? How can you make any meaningful survey of the worlds rivers in a half-dozen programs? It was a challenge that seemed impossiblelike trying to film goonch catfish underwater in the Himalayas, or catch a 250-pound arapaima from the Amazon on a fly rod, or swim with oarfish at night in a mile and a half of water. But wed been there and done all that, in River Monsters season 1, 6 and 8 respectively.

More of a challenge, perhaps, was making a show about the environment that people would want to watch. But here again we had our River Monsters heritage to draw on. Strange as it may seem now, we faced a similar challenge nine years ago. A conventional program about fishing is never going to attract a big audience, or a diverse audience. But River Monsters did both, to spectacular effect, by busting out of existing categories and creating its own genre.

Will Mighty Rivers achieve the same? My fervent hope is that it will achieve more, in its own special way. Thats not just a fishermans blind optimism speaking. A fishermans faith is always rooted in realism. And make no mistake: Im still fishing. But this time Im not just fishing for fishIm fishing for answers, Im fishing for surprises, and Im fishing for hope. And Im fishing for an audience that I know is out there, who are interested in looking at fish and rivers and water and the world in a new way.

Ill see you on the riverbank.

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