Exploring our extraordinary chalk streams

We are unbelievably lucky to be based on the south coast of England, nestled between the beautiful Solent and the South Downs National Park. Not only are we close to the ocean, which we are working hard to protect, but our position at the foot of the South Downs also gives rise to another fascinating aquatic ecosystem – the chalk stream. Chalk streams are rarely found anywhere else in the world. There are only around 200 chalk streams globally, and 85% of them are found in England, mainly here in the south. Today, on the 26th International Day of Action for Rivers, we are exploring and celebrating these crucial ecosystems. 

Chalk streams are rivers that have sprung from underground chalk aquifers, common in the South Downs, and travel through flint and gravel to produce a flow of clean, clear water. This water gives life to biodiversity and allows for farming, towns, and development. The River Ems and River Lavant are both chalk streams and both host an abundance of wildlife. Kingfishers, water voles, otters, and plants and algae found nowhere else in England have been found in the River Ems. And the River Lavant is just as rich in biodiversity, housing water voles, and stream water-crowfoot which is a rarity in Sussex.

The River Ems and River Lavant are both facing threats from different types of human interference. The River Ems has experienced periods of extreme drought, thought to be exacerbated by abstraction that started in the 1960s by Portsmouth Water. The river was rarely dry below Broadwash Bridge along Emsworth Common Road before abstraction from the aquifer. Now, it is common to see the riverbed dry in Westbourne and Emsworth during the summer, which has been intensified by more frequent extremely dry weather. It is important to keep the river flowing to give life to its rich biodiversity. Biodiversity and climate change go hand in hand – a healthy ecosystem with lots of biodiversity helps trap atmospheric carbon through photosynthesising plants and algae, therefore reducing the effects of climate change. The Friends of the Ems are a group of local volunteers who are committed to protecting this valuable chalk stream, they have been working to ensure the water levels stay above healthy levels.

The River Lavant is facing an issue that we are unfortunately familiar with – sewage. Southern Water has been recorded dumping untreated sewage into the River Lavant as far back as 2013, and it doesn’t seem to have stopped in the past 10 years. We have captured footage of sewage leaking into Sheepwash Lane, running into the River Lavant as recently as November 2022. These releases of effluent into the river pollute its clean water with an abundance of nitrates and phosphates. Photosynthesising plankton and algae flourish due to the excess nutrients, creating a thick carpet of green across the water. This may look lush and thriving, but this thick mat of algae creates a water habitat that lacks the oxygen necessary for many species to survive. This algal bloom is threatening the biodiversity in chalk streams such as the River Lavant. The Clean Harbours Partnership is working hard to highlight and ultimately reduce sewage in our local harbours and waterways, along with many other NGOs and pressure groups. We hope to see more action being taken by water companies and the government to protect our precious chalk streams.

It is also imperative to look after our streams and rivers because all rivers lead to the sea. Pollution, either from sewage or plastic litter, that affects rivers will always eventually pollute the sea if nothing is done to prevent it. Rivers are the main source of plastic pollution in the oceans, so keeping our rivers healthy means keeping our oceans healthy, which keeps our planet healthy. It’s a win-win situation!

To find out more about why our freshwater ecosystems are so vital, visit the International Day of Action for Rivers webpage.