voir s ▁will ▁have ▁above ▁average ▁amounts ▁of ▁sed iments ▁and ▁nut ri ents , ▁which ▁can ▁cultiv ate ▁an ▁excess ▁of ▁alg ae ▁and ▁lead ▁to ▁e ut roph ic ation . ▁In ▁addition , ▁res er voir s ▁are ▁required ▁to ▁release ▁a ▁certain ▁amount ▁of ▁water ▁every ▁year ▁to ▁prevent ▁rivers ▁down stream ▁from ▁dry ing ▁up , ▁which ▁would ▁be ▁det r iment al ▁to ▁those ▁e cos ystem s . ▁ ▁T idal ▁energy ▁ ▁T idal ▁energy ▁util izes ▁the ▁gravit ational ▁and ▁kin etic ▁energy ▁of ▁large ▁bodies ▁of ▁water . ▁The ▁physical ▁push ▁and ▁pull ▁of ▁the ▁t ides ▁causes ▁a ▁tur bine ▁to ▁spin , ▁and ▁that ▁tur bine ▁converts ▁the ▁water ' s ▁movement ▁into ▁electric ity . ▁This ▁form ▁of ▁renew able ▁energy ▁produces ▁no ▁poll ution , ▁and ▁takes ▁up ▁little ▁physical ▁space ▁when ▁compared ▁to ▁other ▁forms ▁of ▁renew able ▁energy . ▁It ▁is ▁predict able ▁and ▁reliable ▁form ▁of ▁energy , ▁as ▁most ▁water ▁bodies ▁experience ▁two ▁high ▁t ides ▁and ▁two ▁low ▁t ides ▁per ▁day . ▁This ▁cycle ▁is ▁easily ▁predicted ▁and ▁isn ’ t ▁subject ▁to ▁unexpected ▁changes ▁unlike ▁many ▁other ▁renew able ▁resources . ▁Some ▁systems ▁also ▁har vest ▁energy ▁from ▁tid al ▁curr ents ▁regardless ▁of ▁which ▁direction ▁they ▁are ▁flow ing , ▁allowing ▁the ▁production ▁of ▁energy ▁to ▁go ▁completely ▁un inter rupted . ▁The ▁equipment ▁used ▁is ▁long ▁last ing , ▁with ▁an ▁average ▁lif es pan ▁of ▁ 7 5 -