Chalk streams

The Cam is classified as a chalk stream. Chalk streams are spring-fed with rainfall that has been filtered through Chalk, which makes the water alkaline. This alkalinity gives Chalk streams a particular character and ecology.

Geographers say around 80% of the world’s chalk streams are in England, concentrated in the south and east of the country. Ecologically, Chalk streams are England’s rainforests, our unique contribution to global ecology. Yet they are given scant protection. When pressure groups backed by the World Wildlife Fund (WWF) launched the Chalk Stream Charter in 2013 the UK Govt was blasted for 50 years of shabby environmental stewardship. Sadly, not a lot has changed. 

The Environment Agency, an executive arm of DEFRA (Department for Environment, food & Rural Affairs), is responsible for the health of our rivers. It should be among the UK’s most powerful and well-resourced agencies. It isn’t. The agency is under perpetual pressure from central Govt to facilitate growth of housing. Cuts to its budget and staffing have left the agency a shadow of its former self. 

The Cam is not alone. Unless there is radical action to limit abstraction and a properly funded care plan for all the threatened Chalk streams we are at risk of losing an important engine of biodiversity.


Chalk streams are particularly sensitive to pollution, especially nutrient enrichment from phosphates and nitrates. When regulations are abided by and there is a healthy river flow, the effects are minimised; but as the river level falls so this nutrient enrichment overwhelms the river, accelerating plant growth, killing insect life and crustacea and messing up reproduction cycles.

There can be sudden catastrophic events. In the summer of 2018 a sudden heavy downpour drained an unusually large concentration of pollutants off the fields and roads into the river Cam around the Chesterfords. The water was suddenly robbed of oxygen resulting in thousands of dead fish.