Tides: Impact on nature
Low carbon, but estuaries and sea life feel it
What this tab covers What taking energy from this source does to land, water, air and climate, wildlife and ecosystems, with life-cycle emissions and land use where measured.Tidal power emits little greenhouse gas, but barrages reshape whole estuaries, while tidal stream turbines raise concerns about collision with marine animals, underwater noise and changes to sediment flows.
Life-cycle emissions 17 (range 5.6-28) g CO2e/kWh11 Life-cycle, median and range for ocean energy (tidal and wave), IPCC AR5 Annex IIIEffects on nature
| Area | Effect | Size | How it is reduced |
|---|---|---|---|
| Estuary ecology (barrages) | Closing the Rance estuary for construction killed much of its marine life through salinity swings and sediment build-up; the basin is now a new, fragile ecosystem3 | 3-year closure; recovered to a rich ecosystem by 1976; sand-eels and plaice lost, sea bass and cuttlefish returned, 120 bird species unchanged | Avoid full closure during construction; lagoons and partial structures instead of full barrages |
| Water levels and sediment | Barrages hold water higher and slow the ebb, causing progressive silting in the basin3 | Mean water level in the Rance basin rose 2.5 m; tidal range inside reduced | Operating rules that mimic natural tides; dredging |
| Wildlife collision (stream turbines) | Blade strike and entanglement of marine mammals, fish and diving seabirds10 | Main concern for tidal stream; quantitative collision data from operating turbines remain scarce | Monitoring with cameras and imaging sonar, siting away from key habitats, seal-specific consenting studies |
| Noise and electromagnetic fields | Turbine noise may disturb echolocating whales and dolphins; export cables emit electromagnetic fields4 | Underwater noise can exceed that of offshore wind | Acoustic monitoring around operating devices |
| Climate | Emissions come mostly from steel and concrete in construction11 | Median 17 g CO2e/kWh (range 5.6-28) for ocean energy | Longer plant lives (La Rance has run since 1966) |
The biggest effects come from barrages, which turn a tidal estuary into a managed basin. Sediment, salinity, mudflat exposure and fish migration all change. When the UK government decided in 2010 not to pursue a Severn barrage, it cited cost and risk to public finances alongside the loss of salt- and mudflats used by 30 bird species and expected harm to fish. Tidal stream devices change much less, but the evidence base on collisions and noise is still being built from small arrays.
Sources
- La Rance Tidal Barrage (Annex IV site page) Tethys, Pacific Northwest National Laboratory / OES-Environmental, 2024
- Tidal stream generator Wikipedia, 2025
- Short Science Summary 2024: Collision Risk Tethys / OES-Environmental, 2024
- Climate Change 2014: Mitigation, Annex III Technology-specific cost and performance parameters (Table A.III.2) IPCC Working Group III, 2014