The Swedish government is funding research into the feasibility of using a wind-turbine driven oxygen pump in the Baltic, following studies carried out last year by the University of Gothenburg, which looked at the effect of pumping oxygen-rich surface water to the bottom of two Swedish fjords.

CNN: Can oxygen pump breathe life into ocean 'dead zone?'

The pump storage hydro scheme is designed to "soak up" excess power generated by wind and wave farms, using it to pump water up to a reservoir.

BBC: Highland councillors support Lochaber hydro plan