The 'gin-clear' waters of our local chalk streams support many amazing species, from the kingfisher and the otter to the brown trout and the water vole. With only 210 of these streams found worldwide, it is crucial that we keep them in good condition. Yet while their immense value is widely accepted, how best to preserve them is the subject of great debate.

In the past, a more heavy-handed approach was the norm. Many prior generations viewed nature as something to be tamed or tidied, which invariably meant the frequent use of a hand scythe and later a range of powered machines. But this management style, even if well-intentioned, may be doing more harm than good. Could we, in trying to care for these vulnerable habitats, actually put them under greater pressure?

Much has been written about the ‘man‐made’ nature of our chalk streams, and it is true that they have been heavily modified over the centuries. If left entirely alone, they would look very different within a few short years. It is possible, however, to manage the streams in a way that makes them welcoming for wildlife, pleasant for people, and free to flourish on their own terms. Let’s take a look at how this can be done with minimum intervention.

Natural channels

The first thing to consider is the underlying structure of the stream channels themselves. Over the years, many have been artificial straightened or formed into a U-shape. Others have been ‘perched’, which means their channels have been raised higher than the adjacent land as part of a mill or irrigation system. This can cause multiple issues, most notably leaving banks vulnerable to erosion, breaching, and collapse.

Not all erosion is cause for concern; in fact, in moderate amounts, it is fundamental to the health of a chalk stream habitat. The removal and deposition of material by the water’s flow helps create gentle meanders and varied depth, both of which support biodiversity. The damage occurs when modification or improper maintenance send this natural process into overdrive.

Take the replacement of natural banks with chalk bunds, perhaps to contain a perched channel, provide easier access for fly fishing, or (ironically) tackle erosion. In a natural bank, the chalk bedrock is covered with layers of silt, soil, and gravel that encourage the growth of vegetation. The root systems stabilise the bank, tie in the soil, and shield it from the flow, increasing its resilience.

If a bank is made purely from compacted chalk, however, vegetation will struggle to establish. This risk is heightened in perched channels, where the banks are under greater pressure due to the raised water level. Add to that the burrowing of water voles or signal crayfish, and keeping the channel intact becomes like painting the Forth Bridge! Dropping the water level and tapering the banks may reduce the chance of breaches, but repairs usually involve yet more chalk being added.

Accelerated bank erosion can be not only hazardous for people and livestock, but also highly destructive to wildlife. As the channel gets wider, the flow velocities become slower, leading to an accumulation of fine sediment over what would normally be a clean gravel stream bed. This smothers fish eggs, restricts the growth of flow‐loving water plants, and impacts the survival of many aquatic invertebrates.

Managed river weed

While micro-managing chalk streams can be detrimental, they can benefit from careful cutting of aquatic ‘weed’. Excess nutrients in our local streams, coupled with a lack of tree shade, can result in rampant growth that ultimately chokes the channels. The water level then rises while the flow speed drops, leading to sediment accumulation and sometimes a boom in water parsnip, bur-reed, or mare’s tail.

Knowing if and when to get the cutter out can be tricky, and even experienced river keepers have to make a judgment call based on the current flow and plant growth conditions. But it is hugely important, because if too much weed is cut, the health of both the channel and the marginal zone can be seriously impacted. A little restraint also aids those folks who have to receive and clear large amounts of weed when co-ordinated cuts are taking place upstream.

The holy grail of weed management is leaving enough aquatic plants to provide wildlife habitat, but enough gaps to encourage vigorous flow. This helps to manage water levels and keep the gravelly bed clear of fine sediment, which is essential for the breeding of trout and the invertebrates on which they feed. A diversity of plants is also better than a monoculture of water crowfoot.

Where invertebrates are concerned, it is equally important that these submerged plants are allowed to break the surface. The breeding of iconic and threatened riverfly species like the blue winged olive will be drastically impaired without them. This is because the females need a dry landing spot from which they can creep into the water to lay their eggs. It is therefore no surprise that the population of many invertebrates relies on the availability of this habitat feature.

Access for anglers

As we can see, chalk stream management is a rather knotty topic. It gains extra complexity when we consider those stretches of chalk stream that are dedicated to fly fishing. The dilemma for the river keepers who maintain these parts is how to balance the needs of wildlife with reasonable access for anglers. My own belief is that the needs of plants, bugs, and fish are paramount, and that the right balance may involve a few sections being less attractive to some anglers.

It is worth noting that an abundance of wildlife habitat is essential for any high-quality fishery, and if anglers are up for careful wading then the marginal fringe can be allowed to grow. Where wading is unsafe, this trade-off can be maintained by cutting a path well back from the edge, with the occasional route down to the water. A margin of reeds, rushes and other plants forms an underwater forest, where young fish can find food while shielded from predators and the flow.

Similarly, overhanging branches and fallen woody material need not be tidied away, as fish love to ‘lie’ beneath and between them. If it proves a hindrance then this material can simply be moved instead, but should then be left in its new position. In truth, most of our chalk streams are overly exposed to direct sunlight and would benefit from additional shading by low, dense species like goat willow or hawthorn. The boons would be numerous: habitat for wildlife, cover for anglers, and shade that could help prevent stream overheating and the rampant growth of aquatic weed.

Cherished chalk streams

So what is the main takeaway, when it comes to the management of chalk stream habitats? Well, the ideal strategy essentially boils down to a lighter touch. Recent work on the Rivers Test and Itchen by the Environment Agency, Wessex Rivers Trust, Wild Trout Trust, Watercress and Winterbournes, and several landowners, have also shown how habitat restoration can reduce maintenance requirements by making chalk streams more balanced and resilient to climate change.

Living with a shaggier look – banks brimming with a diversity of native trees and lush foliage; the channel dotted with submerged and emergent weed – will eventually pay dividends. Those parts frequented by anglers will be more capable of sustaining fish like wild brown trout, and therefore require less stocking. We have made much progress in this direction, and the potential for healthier and more productive chalk stream environments is within reach for us all.

If you’re a landowner seeking advice on managing your stretch of chalk stream, why not book a free Wild Trout Trust advisory visit? You’ll receive a written report that highlights any issues and makes recommendations for habitat enhancement. There are also a number of handy guides available on their website. Just looking to explore the wonders of Hampshire’s chalk streams? Check out the many exciting projects of the Watercress and Winterbournes scheme.