The River Thames in London has an enormous tidal change twice a day so it makes sense to try and harness some of that as a renewable energy source.
BBC News – Tidal energy trial in Thames offers glimpse of future
The turbines can operate at a range of depths
A tidal energy farm providing green energy to London could become a reality if a two-month trial proves successful.A tidal turbine is being installed in the River Thames alongside World War II ship HQS Wellington in central London. If the trial proves successful and does not adversely affect the environment, hundreds of turbines could be installed between Kent and London. Energy company Nautricity said a tidal energy farm would generate enough electricity to power 35,000 homes.