Waves are created in the oceans by winds which in turn are driven by the sun by differential heating of the earth's surface. Usable electric power must then be generated by devices such as the "Nodding Duck" (developed at University of Edinburgh) or the "Clam" (developed at Coventry University). The initial costs are high and further development is needed. The UK has fallen behind some other nations due to government decisions in the past.
[also see below the later entry "In 2004"].

Tidal power is also associated with the seas but the moon is the main cause of tides. The energy can be harnessed most easily where there is an estuary and one of the best sites anywhere, is the Severn Estuary. Apart from high constructional costs (estimated at around £10 billion), the creation of a tidal barrage on the Severn to implement such a system would have an environmental impact on wildlife. Conservationists oppose such schemes for this reason but the counter argument says that while some habitats would be destroyed (for example those of waders) others would be created for different species. A relatively recent development is tapping the resources of underwater tidal currents (see Marine Current Turbines Ltd on the Alternative Energy page under the heading of Water Power)
[also see below the later entry "In 2004"].

Hydro power is available by creating dams in stream and river flows. The sun is the driver in such a bio system. Hydro power generation is an established technology and maybe as much as one fifth of the world's electricity is generated this way, which is slightly more than by nuclear generation. The major factor weighing against it is the environmental impact.
Because hydro schemes have a known record, the evidence is indisputable. Where large dams have been constructed, large areas of land are drowned. The results can be lethal for local wildlife and catastrophic for the human inhabitants of that area who become displaced en masse. Very often beautiful landscapes are destroyed and valuable archaeological sites made inaccessible for ever. Two contemporary, infamous projects that illustrate these problems are the Narmada Valley development in Gujurat, India and the Ilisu dam on the Tigris in Turkey. Others are less known such as the Noral Hydro project in Iceland.
There are ways of mitigating such catastrophes such as consultation with the affected population and relevant experts before decisions are made, accompanied by suitable compensating actions afterwards. However, history shows that the forces driving such decisions are not particularly good at democratising the process and of course this would not solve all the problems anyway.
The severity of the aftermath of dam creation is related to the size of the project, large projects create widespread, serious problems. Therefore hydro schemes could be more acceptable, in some cases, if there were several, small distributed systems rather than one big one, unfortunately fragmented systems normally are less efficient.

In 2004, new evidence has come to light which paints a far brighter outlook for wave and tidal power and hence renewable energy in general.
According to The Guardian (John Vidal and Paul Brown, 18 Feb. 2004) the calculation of cost of wave power was vastly overestimated due to a "mistake" in the calculations when a decimal point was moved. This "mistake" happened about twenty years ago but the bad news was that wave power was abandoned and (surprise, surprise!) the nuclear industry benefited. In 2004 the government seems to be taking renewables seriously and modest but significant investments are being made to encourage the development of alternative, renewable energy generators, no doubt spurred on because Tony has contracted to reduce carbon emissions to a target. Work continues to evaluate marine energy with the Carbon Trust putting in £2.5m, aiming for a completion date at the end of the 2004/5 financial year. It gets better because there are now more devices being examined than were previously envisaged, including under-water turbines which take advantage of tidal currents that exist in river estuaries such as the Severn. Additionally the idea of Tidal Lagoons has been introduced. These would trap water and release it in a controlled way through turbines. If these methods could be developed successfully the potential is there for very large scale energy production which could make a significant difference to the energy sourcing in the UK and hopefully obliterate plans for nuclear power generation from the country's strategy. One big factor in the favour of recent marine technologies is that they do not suffer from the criticism of being environmentally visually unattractive, like wind farms. Furthermore their output can be predictably reliable hence countering another specious argument of the pro-nuclear lobby.

In summary: Water power is, in principle, clean because there are none of the six identified polluting gases produced and moreover, the power is genuinely renewable. Nevertheless there can be serious drawbacks where water power is generated on a large scale.
First there is the financial cost, or perhaps this is better described as political will which, often amounts to the same thing. With major projects which require massive R and D investment before profits can be realised, national leadership is often needed to create the impetus to reach an 'escape velocity'. In the UK this has not been forthcoming but perhaps things are changing. The second important penalty is that there are environmental pollutions such as destroying the beauty of the landscape or, perhaps more seriously, the destruction of eco-systems. The scene may change, however, because two new factors have arisen in recent years.
One is the fall from grace of nuclear power (we discuss nuclear power on another page) which had been treated as of greater priority, at the expense of equally attractive alternative and renewable sources such as the ones listed here. The other is the pressure created by the international acceptance that global warming is upon us with devastating consequences looming. We hope that these factors will provide the political will to develop such clean energy sources as the ones above and others identified elsewhere on the main page.