Environmental Impacts of <strong>Dams</strong>From the Falmouth Gazette<strong>and</strong> Weekly Advertiser,Sept. 23, 1785.The damagecaused by damson Ma<strong>in</strong>e’s rivershas been veryhigh.Although dams have provided – <strong>and</strong> <strong>in</strong> many casescont<strong>in</strong>ue <strong>to</strong> provide – valuable services <strong>to</strong> our society,they have done so at a significant cost <strong>to</strong> the orig<strong>in</strong>alecosystems of our rivers <strong>and</strong> streams. <strong>Dams</strong> fundamentallyalter the habitat of a freeflow<strong>in</strong>griver. The damage causedby dams on Ma<strong>in</strong>e’s rivers hasbeen very high.Ma<strong>in</strong>e’s major rivers oncesupported large populationsof sea-run fish <strong>and</strong> eels.Generally, these species areborn <strong>in</strong> <strong>in</strong>l<strong>and</strong> streams <strong>in</strong>freshwater, travel downstream<strong>to</strong> live most of theiradult lives at sea, thenreturn <strong>to</strong> spawn <strong>in</strong> the rivers of theirorig<strong>in</strong>. With the construction of damson Ma<strong>in</strong>e’s rivers, these fish were cut off from theirspawn<strong>in</strong>g grounds <strong>and</strong> their populations began <strong>to</strong> plummet.The wealth of fisheries that once surged <strong>in</strong> Ma<strong>in</strong>e’s rivers iscaptured well <strong>in</strong> his<strong>to</strong>ric records. For example, a commercialfisherman estimated that dur<strong>in</strong>g the 1870s more than 30,000Atlantic salmon were harvested each year from the Kennebecbelow Bath alone.But the construction of dams <strong>to</strong>ok a <strong>to</strong>ll on these l<strong>and</strong><strong>in</strong>gs. Thefirst major dam on the Kennebec <strong>River</strong> <strong>in</strong> 1837, for example,resulted <strong>in</strong> dramatic <strong>and</strong> deep reductions <strong>in</strong> fish populations.With<strong>in</strong> a decade, l<strong>and</strong><strong>in</strong>gs of salmon, herr<strong>in</strong>g, <strong>and</strong> sturgeondropped <strong>to</strong> a small fraction of their levels before the Augusta damwas built. A man who reported catch<strong>in</strong>g 500 salmon at Augusta <strong>in</strong>1838, reported that by 1850 a good year might br<strong>in</strong>g four or fivesalmon.Above: <strong>Dams</strong> create an impenetrable wall for upstream fish migration.Fish passage systems have generally served as poor substitutes <strong>to</strong> freeflow<strong>in</strong>grivers.Right: The State has taken enforcementactions <strong>in</strong> recent years aga<strong>in</strong>stdam owners <strong>in</strong> Ma<strong>in</strong>e wherethous<strong>and</strong>s of fish have been killedwhile pass<strong>in</strong>g through turb<strong>in</strong>es.Left: Alewives weretrapped each spr<strong>in</strong>gbelow Edwards Dam,until the dam’s removal<strong>in</strong> 1999.8 A Citizen’s <strong>Guide</strong> <strong>to</strong> <strong>River</strong> Res<strong>to</strong>ration
Recent research has documented that the water s<strong>to</strong>red beh<strong>in</strong>da dam has neither the habitat of a river, nor the habitat of a naturallyoccurr<strong>in</strong>g lake. As a result, dams produce an ecosystem that isnot well designed for the species that occur <strong>in</strong> either of thesehabitats.Environmental impacts of damsLeft: “Convert<strong>in</strong>g a river <strong>to</strong> a lakecauses many river<strong>in</strong>e species <strong>to</strong>perish. Many studies havedocumented drastic decl<strong>in</strong>es <strong>in</strong>diverse mussel communitiesfollow<strong>in</strong>g the construction ofdams.”The Freshwater Mussels of Ma<strong>in</strong>e,Ma<strong>in</strong>e Department of Inl<strong>and</strong> Fish<strong>and</strong> Wildlife, 2000• <strong>Dams</strong> block the movement of river life – prevent<strong>in</strong>g fishmigration, halt<strong>in</strong>g the flow of plants <strong>and</strong> nutrients, <strong>and</strong> curb<strong>in</strong>gdownstream recreational use.• <strong>Dams</strong> slow rivers – <strong>in</strong>terfer<strong>in</strong>g with the steady flows that somespecies, such as salmon, need <strong>to</strong> flush young fish downriver <strong>and</strong>guide them upstream years later <strong>to</strong> spawn.• <strong>Dams</strong> flood upl<strong>and</strong> areas – by creat<strong>in</strong>g a reservoir that <strong>in</strong>undatesl<strong>and</strong> that previously served as terrestrial habitat, <strong>and</strong> mayhave been valued floodpla<strong>in</strong>s.• <strong>Dams</strong> alter water temperatures – usually <strong>in</strong>creas<strong>in</strong>g temperaturesby slow<strong>in</strong>g flow; sometimes decreas<strong>in</strong>g water temperaturesby releas<strong>in</strong>g cooled water from the reservoir bot<strong>to</strong>m. Temperatureirregularities can harm aquatic life.• <strong>Dams</strong> alter tim<strong>in</strong>g of flows <strong>and</strong> cause water level fluctuation –by withhold<strong>in</strong>g <strong>and</strong> then releas<strong>in</strong>g water <strong>to</strong> generate power.These releases can act like a firehose wash<strong>in</strong>g away plants <strong>and</strong>animals downstream, erod<strong>in</strong>g soil <strong>and</strong> vegetation, <strong>and</strong> flood<strong>in</strong>gor str<strong>and</strong><strong>in</strong>g wildlife, disturb<strong>in</strong>g fisheries <strong>and</strong> waterfowl. Theseirregular releases destroy seasonal flow variations that triggernatural growth <strong>and</strong> reproduction cycles <strong>in</strong> many species.• <strong>Dams</strong> reduce dissolved oxygen – reduc<strong>in</strong>g circulation of thewater <strong>and</strong> <strong>in</strong>creas<strong>in</strong>g its temperature, which can result <strong>in</strong> lessoxygen than is necessary for the survival of many species.• <strong>Dams</strong> hold back silt, debris, <strong>and</strong> nutrients – by slow<strong>in</strong>g flows,dams can allow silt <strong>to</strong> collect on river bot<strong>to</strong>ms <strong>and</strong> bury fishspawn<strong>in</strong>g habitat. <strong>Dams</strong> also trap gravel, logs <strong>and</strong> other debris,Right: Wild Atlanticsalmon like this one onCobbosseecontee Stream<strong>in</strong> 1997, are nearly ext<strong>in</strong>ct<strong>in</strong> the U.S., <strong>in</strong> part due <strong>to</strong>the construction ofimpassable dams.elim<strong>in</strong>at<strong>in</strong>g their availability downstream as food <strong>and</strong> habitat.• <strong>Dams</strong> can harm fish – by follow<strong>in</strong>g currents downstream, fishcan be drawn <strong>in</strong><strong>to</strong> <strong>and</strong> cut up by power turb<strong>in</strong>es.• <strong>Dams</strong> <strong>in</strong>crease preda<strong>to</strong>r risk – warm, murky reservoirs oftenfavor preda<strong>to</strong>rs of naturally occurr<strong>in</strong>g species. In addition,passage through fish ladders or turb<strong>in</strong>es can <strong>in</strong>jure or stun fish,mak<strong>in</strong>g them easy prey for fly<strong>in</strong>g preda<strong>to</strong>rs like gulls <strong>and</strong>herons.• <strong>Dams</strong> reduce productivity of estuaries <strong>and</strong> bays – becausethere are fewer juvenile fish due <strong>to</strong> the <strong>in</strong>accessibility ofspawn<strong>in</strong>g grounds <strong>to</strong> sea-run fish. Ma<strong>in</strong>e’s Department ofMar<strong>in</strong>e Resources estimates that for every return<strong>in</strong>g adult fish,300-400 juveniles return <strong>to</strong> our estuaries <strong>and</strong> bays each year,add<strong>in</strong>g tremendously <strong>to</strong> the ocean food cha<strong>in</strong>.More than 600,000miles of the nation’srivers <strong>and</strong> streamshave been floodedbeneath waterss<strong>to</strong>red beh<strong>in</strong>d dams.A Citizen’s <strong>Guide</strong> <strong>to</strong> <strong>River</strong> Res<strong>to</strong>ration 9
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