This question most recently perplexed roomfuls of politicians when the European Union tried to devise a fishing policy for 2001 to provide something to fish for in future. Evidently none of them had been looking into the cooling systems of power stations. Their seawater intake pipes may not be salubrious places. However, they hold the sorry secret of where many fish end up and show that it is not just fishermen who are to blame for emptying the sea.
All power stations have to be cooled.
The easiest way to cool plants that generate vast heat is to use water. Seawater is free. That is why, hunkered around the British coastline, squat the familiar colossi of power plants, mostly built long ago. Cooling water needs to be screened. You cannot have salmon fricassee hurtling around power plants as a coolant.