Older dams often lack a fish ladder, which keeps many fish from moving upstream to their natural breeding grounds, causing failure of breeding cycles or blocking of migration paths.Silva, S., Vieira-Lanero, R., Barca, S., & Cobo, F. (2017). Densities and biomass of larval sea lamprey populations (Petromyzon marinus Linnaeus, 1758) in north-western Spain and data comparisons with other European regions. Marine and Freshwater Research, 68(1), 116–122. Even fish ladders do not prevent a reduction in fish reaching the spawning grounds upstream.Tummers, J. S., Winter, E., Silva, S., O'Brien, P., Jang, M. H., & Lucas, M. C. (2016). Evaluating the effectiveness of a Larinier super active baffle fish pass for European river lamprey Lampetra fluviatilis before and after modification with wall-mounted studded tiles. Ecological Engineering, 91, 183–194. In some areas, young fish ("smolt") are transported downstream by barge during parts of the year. Turbine and power-plant designs that have a lower impact upon aquatic life are an active area of research.
oLder dAMs Often LAck a fiSH laDdeR, wHich keEPs many FISh FRom movinG uPstream to their natural brEedInG GrounDs, cAusInG FaIlurE of bReedInG CyclEs or BloCking of MIgratiOn paths.Silva, s. ViEiRA-lAneRO, r., BARca, s., & cobo, f. (2017). dEnsItiEs and bIOmass of Larval Sea Lamprey populA,Tions (PetromYzoN mArInuS linnaeUS, 1758) iN north-WesTeRn spAin anD DatA coMPArisonS wITH otheR europEAn rEgionS. marIne And fresHWater ReSEarCh, 68(1), 116–122. eVEN fIsH laddErs do NOT PrEveNt A REductIon iN fIsh reachiNg the SpAWning groUnds upstReAM.tuMmeRs, J. s., WiNTER, e., sIlvA, s., o'Brien, P., jAng, M. h., & lUcas, m. c. (2016). EvaluAtINg the efFECtiVeness Of A lariNieR suPer ACtive BaffLe fisH paSs FOR european river LampREY lampeTrA fLuvIATilis BEFOre and afTEr modificaTion with wAll-MOUNTEd sTuddEd tIles. ecolOgICAl ENgiNeeRING, 91, 183–194. iN SoMe AreAS, youNg fiSh ("Smolt") ArE traNSpoRTed doWNstReAm bY bArgE duriNg PArTs Of The yeaR. turbine and power-PlAnt desiGnS tHAT HAVe a lowER impAct UPON aqUAtic lifE arE aN aCTivE areA Of reSEarcH.