Editing River Mole (section)

===Biodiversity===
The [[marsh frog]] (''Pelophylax ridibundus'', a non-native species introduced from Europe in the 1930s) is now commonly found in the upper Mole and its tributaries around [[Newdigate]] and Gatwick.<ref name=little_book_Surrey>{{cite book |last= Matthews |first= Rupert |year= 2010 |title= The little book of Surrey |location= Stroud |publisher= History Press |pages= 118–119 |isbn=9780752456331}}</ref> There is no evidence that the presence of the frogs has had a deleterious effect on [[indigenous (ecology)|indigenous]] amphibians.<ref>{{cite web |url= http://surrey-arg.org.uk/cgi-bin/SARG2ReptileSpeciesData.asp?Species=Marsh_Frog |title= Marsh Frog |author= Wycherley J |date= January 2008 |work= Database of amphibian species |publisher= Surrey Amphibian and Reptile Group |access-date= 7 February 2010 |archive-url= https://web.archive.org/web/20111004062024/http://www.surrey-arg.org.uk/cgi-bin/SARG2ReptileSpeciesData.asp?Species=Marsh_Frog |archive-date= 4 October 2011 |url-status= live }}</ref> A second non-native species, the [[edible frog]] (''Pelophylax'' [[klepton|kl.]] ''esculentus'') was introduced to a site at [[Newdigate]] in the early 1900s. It has in 2008 been recorded in tributaries of the River Mole at [[Capel, Surrey|Capel]] and [[Brockham]].<ref name=little_book_Surrey/>

[[File:River Mole from Common Meadow, Leatherhead.jpg|thumb|River Mole from Common Meadow, Leatherhead]]
The River Mole has the most diverse fish population of any river in England.<ref name=EA_fish/> The '''Gatwick Stream''' is dominated by coarse fish such as [[brown trout]], [[brook lamprey]], and [[European eel|eel]]. In 2003, the upper River Mole near Meath Green Lane, Horley, was enhanced to create a gravel [[Spawn (biology)|spawning]] area to encourage [[European chub|chub]] and [[Common dace|dace]] in addition to [[Common roach|roach]].<ref name=CAMs/> In 1974 [[zander]], a non-indigenous coarse fish native to Europe, were introduced legally to Old Bury Hill Lake which supplies the Pipp Brook. Zander have been caught in the Lower Mole below Dorking since the 1980s.<ref>{{cite journal |author=GH Copp |year=2003 |title=Introduction and establishment of the pikeperch ''Stizostedion lucioperca''(L.) in Stanborough Lake (Hertfordshire) and its dispersal in the Thames catchment |journal=The London Naturalist |volume= 82 |pages=139–153 }}</ref>

In the Mole Gap between Dorking and Leatherhead the river supports populations of chub, dace, [[barbel (fish species)|barbel]], and brown trout. Both barbel and brown trout are extremely sensitive to water quality and pollution. Below Leatherhead the river has historically supported larger predatory fish including chub, [[European perch|perch]], [[Northern pike|pike]], and eels, however in recent years chub and eel numbers have begun to decline. North of Esher the old river channel is dominated by [[Hydrocotyle umbellata|floating pennywort]], a highly invasive weed, which cuts off all light to the river bed, reducing oxygen levels and resulting in a poor habitat for fish. The Ember flood relief channel has a diverse fish population, including chub, dace, roach, [[Common bleak|bleak]], large pike and barbel.<ref name=CAMs/> At the [[confluence]] of the Mole and the River Thames at Hampton Court Palace it is possible to catch a wide variety of [[coarse fish]] species.<ref name=CAMs/>

The geographical distribution of many species of [[invertebrate]] in the river reflects the geology of the catchment area. Viviparid [[snails]] and water scorpions (of the genus ''Nepidae'') are commonly found where the river runs over the [[London Clay]]. Crayfish are common in areas associated with high [[alkaline|alkalinity]], particularly around Brockham, and the tributaries which run over the [[Weald Clay]] provide an excellent habitat for [[stoneflies]], [[Trichoptera|caddisflies]], fast swimming [[mayflies]] and [[beetles|riffle beetles]].<ref>Ruse LP (1996) Multivariate techniques relating macroinvertebrate and environmental data from a river catchment ''Water Research'' 30 (12) 3017–3024</ref>
The [[beautiful demoiselle]] (''Calopteryx virgo'') disappeared from the River Mole during the 1960s owing to deteriorating water quality, but has since recolonised.<ref name=sbdp>{{cite web |url= http://www.surreybiodiversitypartnership.org/xwiki/bin/view/Wetland/ActionPlan |title= Wetland Action Plan |author= Cousins D |date= March 2007 |work= Priority Habitats |publisher= Surrey Biodiversity Partnership |access-date= 8 February 2010 |archive-url= https://web.archive.org/web/20080905131921/http://www.surreybiodiversitypartnership.org/xwiki/bin/view/Wetland/ActionPlan |archive-date= 5 September 2008 |url-status= live }}</ref> The [[white-legged damselfly]] (''Platycnemis pennipes'') is also found along the river, and the [[downy emerald]] (''Cordulia aenea'') is found between [[Box Hill, Surrey|Box Hill]] and Leatherhead.<ref name=sbdp/><ref>P. Follett (1996) Mole Valley Natural History Audit: Survey of ''Odonata'' - Dragonflies and Damselflies</ref>  The Mole is one of only three locations in England where the river shingle beetle (''Meotica anglica'') is found.<ref>{{cite web |url= http://jncc.defra.gov.uk/PDF/UKBAP_Tranche2-ActionPlans-Vol6-1999.pdf |title= Grouped Plan for River Shingle Beetles |author= Williams M |date= October 1999 |work= UK Biodiversity Group Tranche 2 Action Plans |publisher= UK Biodiversity Action Plan |access-date= 7 February 2010 |archive-url= https://web.archive.org/web/20110704193928/http://jncc.defra.gov.uk/PDF/UKBAP_Tranche2-ActionPlans-Vol6-1999.pdf |archive-date= 4 July 2011 |url-status= live }}</ref>

A nationally scarce species which is locally common on the River Mole is the [[Cuscuta europaea|greater dodder]] (''Cuscuta europaea''), a [[parasitic plant]].<ref name=little_book_Surrey/>