Chalk Streams in Three Rivers


In our District, we are privileged to host three chalk rivers, all of which meet in Rickmansworth and gave rise to the name of the District – Three Rivers. These rivers represent 1.1% of all chalk streams globally - there are only 260 chalk streams on Earth!   These streams emerge from underground chalk aquifers and typically flow over flinty gravel beds. This ensures their cleanliness but also endows them with dissolved iron and magnesium minerals. Aquatic plants such as Flag Iris and Water Crowfoot thrive on their banks; the brilliant sulphur coloured Yellow Dun Mayfly and Green Drake Mayfly flourish in their ultra-clean waters; while otters, kingfishers and water voles make their homes there.

  • The River Gade rises from a spring in the Chiltern Hills in Buckinghamshire and flows into Three Rivers after passing through Cassiobury Park in Watford.
  • The River Chess rises near Chesham and flows for 11 miles to its confluence with the Colne in Rickmansworth as well.
  • The River Colne which has its source near North Mymms is fed by numerous chalk rivers including the Gade, Chess, Ver and Misbourne finally discharging at its’ confluence with the Thames at Staines.

Sadly, these rare and precious habitats are under threat from water pollution, over-abstraction and global warming. Since 1985 there has been a 75% increase in household water use, and as a result abstraction rates have soared across the country. This is especially true in Three Rivers where we consume 10 litres more water per person each day than the national average.

Global warming is triggering more heatwaves which in turn dries out streams further, resulting in fewer than a fifth of all England’s rivers being considered in a healthy condition including our precious chalk streams. In the 2019 drought 67% of the chalk streams in the Chilterns dried out. This is killing vulnerable wildlife that depend on these habitats for their survival.                                                                               

With the encouragement of the Chiltern Chalk Stream Project two abstraction sites on the Chess have been closed and Affinity water are working towards ending all unstainable abstraction.

For more information on the rivers visit:


Clean Water


Affinity manages all of our clean water, and is working very hard to protect our chalk streams. Last year Affinity voluntarily stopped abstracting water from 2 boreholes on the River Chess and is committing to ending environmentally unstainable abstraction from these precious water catchments. Thames Water will stop abstraction from another borehole in the upper reaches of the Chess in 2024. These actions will increase flow, and improve the health of the river. However, far more needs to be done and we can all help. Affinity have launched a campaign across Hertfordshire called ‘Save our Streams’ to help us all save 10 litres of water a day. If you sign up you can receive a range of free water-saving devices for your home and encouragement to find ways to save water. If we all save 10 a day it will help preserve the wildlife living in our chalk streams.



Under the Bathing Water Directive (BWD) the River Chess is not a Designated Bathing Water. Members of public and businesses should be aware that rivers are not sterile environments and bacteria are widespread both upstream and downstream of the sewage works at all times. All water users should take relevant health and safety measures.

If you do choose to swim in rivers or canals you do so at your own risk.

There are many factors to consider when interacting with rivers. Safety advice can be sought from the Rivers Trust or Royal Life Saving Society.