Many of us may have visited a chalk stream on a sunny summer day, the water clear and bubbling, ducks chattering away, and pollinators busy about their work. We may have strolled past an unassuming patch of dry sediment and thought nothing of it, barren as it looked. Little did we know, it was in fact a winterbourne, a habitat harder to identify and indeed rarer than downstream chalk stream reaches with year-round flow.

What is a winterbourne?

For centuries we have known that chalk streams are often several kilometres longer in winter than in summer. In recent years, however, it has become clear that the sections that go through flowing and dry phases are home to complex wildlife communities. This transition can be attributed to increased rainfall, and the rise in groundwater levels that follows.

Ever-changing habitats

Much like a rockpool, winterbourne habitats are ever-changing, albeit on a much slower timescale. In their flowing phase, they support all the iconic chalk stream wildlife you would expect, such as kingfishers, water crowfoot, brown trout, and damselflies. However, the intermittent flow of a winterbourne has even greater biodiversity than the constantly flowing sections downstream. We can also find several invertebrates that are so highly specialised to life in a winterbourne that they are very rare in other habitats! 

Their inconspicuous dry phases make winterbournes especially vulnerable to being damaged by human activity – such as mowing and livestock trampling. There are even cases of roads being built over winterbournes in their dry phases, which then inevitably flood once groundwater levels rise.  

Challenges 

Drought and abstraction, topics which were in the news a lot in 2025, also impact winterbournes by reducing water flow. Reduced flow is often associated with warmer water temperatures which can be harmful to our wildlife. A natural, unmodified shape and form can make winterbournes more resilient than modified channels in their flowing phase, against the extremes of weather associated with both yearly variations and long-term trends, including those like climate change. Thus, it is more important than ever that we protect winterbournes. This begs the question, how do we protect a highly specialised habitat that may appear hidden for half of the year?  

Launch of the New Winterbournes Guidance Document

Restoration for channels that have been changed from their natural state is a great first step, and this work has already begun in our area.

In collaboration with a range of partners and stakeholders, the Watercress and Winterbournes Landscape Partnership Scheme is working to restore and improve management of these habitats as well as creating a Winterbournes Guidance Document, which you can find below.

To the many of us who enjoy connecting with our local wildlife and habitats, we often think of winter as the time when everything slows down, and for the most part we are right. Winterbournes, however, are a mysterious and wonderful exception to that rule. They show us that our incredible chalk streams are living ecosystems that ebb and flow with the very seasons themselves.

It is often the quietest wonders of the natural world that are overlooked the most. We must recognise these habitats for the unique treasures that they are, protecting and managing them accordingly. 

So, come the cold and dark of winter this year, we should all encourage ourselves to put on a warm coat, and take a walk along the newly flowing stretches of chalk stream. Be sure to visit again in summer and take a closer peek at the hub of activity in the dry phase, for it is the mosaic of all the phases that makes the winterbourne so rare and special.