The ocean holds great potential as a source of renewable energy from waves, tides, or salt and temperature gradients. The European Union alone estimates that by 2050 up to 10% of its energy demands could be fulfilled by energy harnessed from the oceans. Research on this sustainable energy however, lags when compared to alternative energy sources and concerns have been raised regarding its potential effects on aquatic ecosystems and biodiversity. Developing innovative strategies to harness energy from the oceans, or further understand its environmental impact, will contribute to realise its full potential.