When Rob Cunningham was growing up in Norfolk, England, he would sometimes go fishing with a friend on the banks of a river where the water was crystal clear. “I was a rubbish fisherman,” he says. “I never really caught any, but I’d see loads of trout.” The spot on the River Wensum was idyllic, he says, with strands of water-crowfoot—a kind of ranunculus—blooming on the water’s surface.
It was only years later, as Cunningham was studying environmental science in another region of England, that he would come to realize how unusual rivers like the Wensum really are. Known as “chalk streams”—a globally rare type of waterway found almost exclusively in England—these rivers’ specific features both create rare biodiverse habitats and make them uniquely vulnerable.
Today, as the director of The Nature Conservancy’s Resilient Watersheds program in Europe, Cunningham is trying to protect rivers like these throughout Norfolk via a water fund.
Launch in 2024, the Norfolk Water Fund is a collaboration of multiple local and regional partners that pairs investors, residents and agencies to finance projects designed to protect the quantity and quality of the area’s water. (Read more about the water fund in the latest issue of Nature Conservancy magazine.)
But what exactly are the chalk streams that run through that region?
Burbling up from aquifers formed in chalk layers that date back to the Cretaceous Period, these rivers exist only where chalk sits close to the Earth’s surface. That’s why of the 200-odd identified chalk streams in the world, nearly all of them are found in England, where 66 million years ago a shallow seabed collected the skeletons of aquatic creatures—the makings of chalk.
About 15,000 years ago retreating glaciers carved channels into this old layer of chalk. Rainfall seeped into this chalk aquifer and eventually emerged as springs that still today provide most of the water in these streams.
“It can take anything from a matter of years to decades for rainwater to move through the chalk and then emerge into the river,” Cunningham says. “So you’ve got this massive filtration system.” The result, when the streams are healthy, is clear water, low nutrients, remarkably consistent temperatures and a gravel creek bottom left over from the retreat of glaciers in the last Ice Age.
Those conditions have made these rivers ideal habitats for trout and at one time, Atlantic salmon too. The endangered water vole uses chalk streams and insects like the banded demoiselle thrive near them. In the summer, blooming water-crowfoot indicate a healthy chalk stream. In southern England, some chalk streams have become world-renowned for their flyfishing opportunities. They can be, as Cunningham put it, idyllic and slow.
“We often think about rivers being shaped by storm events and floods,” he says. “But with a chalk stream, all of that carving happened at the Ice Age. They’re actually really low energy, so they don’t have enough energy to reshape themselves.”
All of those factors make them vulnerable to pollution and development. The loss of trees along riverbanks and the increase in intensive agriculture nearby has led to more water running into the streams, carrying silt and nutrients from inorganic fertilizers. Because the aquifers hold so much clean water, they’ve been over-exploited. And unlike many rivers that, though straightened, carve new paths through erosion, chalk streams aren’t strong enough to return to their original paths on their own.
Restoring these chalk streams involves using historic maps to learn where the rivers once traveled. “It’s essentially like a detective story,” Cunningham says, “a real combination of art and science and history.”
Chalk stream restorers use those maps to help plan where to “re-wiggle” artificially straightened streams. They also use hydrological models to help decide how deep to dig a channel. In some cases, they’ll take soil cores to identify the original channels: Because the streambeds were first dug 50,000 years ago as glaciers left behind gravel, some restorers have identified those original channels in part by finding that gravel again.
In Norfolk this restoration work involves TNC along with residents, the water utility, the local council and many other partners. It involves creating landscape buffers, holding water in “leaky” ponds where soil overlays a chalk aquifer, planting trees and more.
The process can look worse before it gets better. “There’ll be mud everywhere and it looks like you’ve created a disaster,” Cunningham says. “But then it’s amazing how quickly life comes back.”
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