Tidal power - Disadvantages
  

• Environmental Damage. There is considerable effect on the ecosystem. The exchange of water volume between a basin and the sea is reduced, this leads to the potential for increased pollution, because pollution is left accumulating in the basin. Also, because the exchange of volume is reduced, salinity of the basin decreases and sediment accumulation increases. Basically, anything we place in the water can and does affect the ecosystem.

• Fish population. Even with the best barrage designs, fish mortality rate per pass through the barrage is about 15%. Solutions to resolves this problem have either failed or are too impractical and too expensive.

• Time of day. Tides are predictable, but power stations only generate power when the tide is flowing in or out of the basin, which only happens during certain times of the day.

• Economical. Startup costs to build a tidal energy plant is high, but the maintenance costs are very low. This means that you will not see profits for a few years, causing some investors to back out of the project. This can be seen as both an advantage and disadvantage, depending upon desired profit returns.

Do a search on google: