RiverPollution 　　Itseemsthatalmosteverydaythereisanotherstoryaboutpollutionofoneformoranother,inthefoodweeat,thewaterwedrinkandtheairwebreathe.Veryoftenourownactionsleadtothatpollutionandinmanycaseswecandosomethingaboutit.Thesenotesexplainhowyoucaninvestigatepollutionandadviseonpositiveactiontoimproveourrivers. 　　Over97%ofallthewateronEarthissaltyandmostoftheremaining3%isfrozeninthepolarice-caps.Theatmosphere,rivers,lakesandundergroundstoresholdlessthan1%ofallthefreshwaterandthistinyamounthastoprovidethefreshwaterneededtosupporttheEarth'spopulation.Itisestimatedthat,withtheexpectedincreaseinpopulation,therewillbea200%increaseinworldwaterneedsbytheyear2000.Freshwaterisapreciousresourceandtheincreasingpollutionofourriversandlakesisacauseforalarm. 　　Mostfreshwaterpollutioniscausedbytheadditionoforganicmaterialwhichismainlysewagebutcanbefoodwasteorfarmeffluent.Bacteriaandothermicro-organismsfeedonorganicmatterandlargepopulationsquicklydevelopusingupmuchoftheoxygendissolvedinthewater.Normallyoxygenispresentinhighquantitiesbutevenasmalldropinthelevelcanhaveaharmfuleffectontheriveranimals.Animalscanbelistedaccordingtotheirabilitytotoleratelowlevelsofoxygen.Inthefollowinglistanimalswhichindicateahighlevelofdissolvedoxygenareatthebeginningwhileanimalsindicatingalowlevelofoxygenareattheend:stone-flynymphs,mayflynymphs,freshwatershrimps,freshwaterhoglice,bloodworms,tubifexwormsandrat-tailedmaggots. 　　Ifyouseedeadfishfloatingontheriverornoticethatthewaterisdiscolouredandsmellyanyoneofthefollowingformsofpollutionmaybethecause: 　　fertilisers 　　industrialwaste 　　oil 　　warmwater 　　AllincidentsofriverpollutionshouldbereportedtothePollutionControlofficerattheWaterAuthoritygivingasmuchdetailasyoucan:date,time,exactplaceandpreciselywhatyousaw. 　　a)Fertilisers 　　Iflargeamountsoffertiliserorfarmwastedrainintoarivertheconcentrationofnitrateandphosphateinthewaterincreasesconsiderably.Algaeusethesesubstancestogrowandmultiplyrapidlyturningthewatergreen.Thismassivegrowthofalgae,calledeutrophication,leadstopollution.Whenthealgaedietheyarebrokendownbytheactionofthebacteriawhichquicklymultiply,usingupalltheoxygeninthewaterwhichleadstothedeathofmanyanimals. 　　b)IndustrialWaste 　　Chemicalwasteproductsfromindustrialprocessesaresometimesaccidentallydischargedintorivers.Examplesofsuchpollutantsincludecyanide,zinc,lead,copper,cadminandmercury.Thesesubstancesmayenterthewaterinsuchhighconcentrationsthatfishandotheranimalsarekilledimmediately.Sometimesthepollutantsenterafoodchainandaccumulateuntiltheyreachtoxiclevels,eventuallykillingbirds,fishandmammals. 　　Occasionallypoisonoussubstancesaredeliberatelydumpedintoriversandifyouseethisso-called'fly-tipping'goingontaketheregistrationnumberofthevehicleandifpossiblethenameofthefirm.Reportthemattertothepolicewhowillthentakeitfurther. 　　c)OilPollution 　　Ifoilentersaslow-movingriveritformsarainbow-colouredfilmovertheentiresurfa