C
haracterisedbygin-clearwaters,
flowingovergravellybottoms
throughemerald-greenbedsof
aquaticplants,chalkstreamsare
a quintessentialhabitatofthe
pastoralEnglishlowlands.Largepartsofthe
UKdon’thavetheseveryspecialwaterways,
andthat’sdowntogeology.
Thesealkalinestreamsandriversare
notjustworld-renownedfortheirfly-fishing,
butalsocelebratedinculture.Thewriter
IsaacWalton,forexample,whois considered
thefatherofangling,tookinspirationfrom
hisfishingtripsalongchalkstreamswhen
penningTheCompleatAngler, firstpublished
in1653.ArtistJohnConstablefamously
capturedthebeautyoftheHampshireAvon
inhis 1831 paintingofSalisburyCathedral,
now on display at Tate Britain.Morerecently,a 2014reportbyWWF
identifieda totalof 224 Englishchalk
streamsorrivers,alllocated
alongthebandofchalkthat
sweepsdiagonallyacrossthe
eastandsouthofthecountry.
If youthinkthatsoundslike
a decentcount,astonishingly
it’s 85 percentoftheglobaltotal.
Withtheremaining 15 percent
innorthernFrance,it wouldn’t
behyperboletosaychalk
streamslikeoursdon’texist
anywhereelseintheworld.
Allchalkstreamsemanate
fromundergroundaquifers.
Thewaterthatbubblesoutof
thespringshasbeenconverted
from rainwater falling on chalkyhillstochalk-waterbythetransformative
processofpercolation.Asit becomes
purifiedandfortifiedwithmineralsonits
journeythroughthechalkybedrock,the
crystal-clearproductthatresurfacestends
tobecool,witha temperatureofabout
10°C.Beingrelativelycold,thewater
canholdhigherconcentrationsof
life-giving,wildlife-enhancing
oxygen,allthewayfromsource
tomouth.
Moreover,theflowremains
reasonablyconstant,irrespective
ofseason.Thissteadyflowof
cold,clearwatercoursingthrough
meandering,gravellychannels
createsa richecosystem.Thewriter
CharlesRangeley-Wilsonlikens
chalk streams to a “watery Garden of18 BBC Wildlife August 2020WILDLIFE WATCHING
InhisseriesofgreatplacestowatchwildlifeintheUK,thestarofBBC
One’sTheOneShowthismonthturnsourattentiontocrystal-clear
waters that create a habitat that’s almost exclusive to Britain.MIKE DILGER’S
CHALK
STREAMS