Packham takes a plunge into the River Wensum to explore wildlife
Presenter Chris Packham took a unique look below the surface of the River Wensum to explore its fish stocks with underwater filming expert Hugh Miles.
In the mineral-rich, chalk-stream water of the river's upper-reaches they found dace and the rare brown trout.
In the middle-reaches, they discovered minnows are ubiquitous alongside its predators the perch and the pike.
The cameras also spotted roach, whose numbers in the Wensum have depleted because of disease and dredging.
"It's really fascinating how so many different species of fish can all feed in the same small area of river," said Chris.
"Rivers aren't just beautiful, they're great places for wildlife," said Hugh.
"From my short journey down the Wensum there's just as much wildlife below the surface as above, probably even more," he added.
Containing around 30 different species of fish, the River Wensum is also home to one of the largest barbel in Britain, found in the waters near Lyng.
The River Wensum has an abundance of wildlife beneath the surface
During his 50-year career getting up-close to capture wildlife, Hugh Miles, from London, has filmed snow leopards in the Himalayas and polar bears in the Arctic.
However, after spending many of his childhood holidays on the Norfolk Broads, he decided to take on a new challenge and focus on becoming a specialist in underwater filming.
"It's a passion of mine - the fish of rivers and lakes in Britain - and it was my mission in life to raise the profile of fish and their importance to the wider world," said Hugh.
"The Wensum's a wonderful river - it's a rare river in British terms with its chalk streams.
"The water's incredibly clear, there's lots of weed growth which provides homes for insects and those insects in turn provide food for fish.
"There's a wonderful variety of fish in the river."
However, despite its diversity of fish Hugh is concerned that the habitats of the Wensum have become badly damaged and hopes they can be saved and expand in the future.
"Fish are really important because so much else depends on them," said Hugh.
You wouldn't have kingfishers, herons, grebes, egrets or otters if there weren't healthy fish populations, and that's one of the concerns about the Wensum.
"It's sadly very much on the decline and the signs are desperate for the future of the Wensum because of what's happened in the past."
large scale renovation
of the River Wensum in Norfolk is under way by the Environment Agency and Natural England to try to provide a better ecology for the river.
It has been criticised for being dug too deep, wide and straight causing habitats to be lost.