So scientists are trying to scare the fish away from the inlets by shouting at them.
Staff at the Fawley Aquatic Research Laboratories in Southampton say that fish do not deserve their cold and silent reputation, and are actually quite talkative. By dangling a microphone in a water-filled plastic bag suspended from a frame to make a piscine recording studio, they can hear the fish talking to each other in brief bursts, some of which can be measured in fractions of a second.
Males and females talk at the same rate, apparently, although most talking is done when the sexes are mixed. Courting pairs are very vocal, and more conversations take place at night and when the water is warmer.
Sadly, the scientists have no idea what the fish are saying but they hope that if they replay the right sounds at a distressingly high volume near the water inlets, the fish might be scared away. The analogy used is that of the noise at a heavy metal rock concert - loud enough to be uncomfortable, but not loud enough to do actual damage.
It is hoped that the tests, which have been under way for more than a year, will enable scientists to identify the right sort of noises to play to the various species of fish. Prototypes have already been tested at an indoor swimming pool at the laboratories and at a nuclear power station.
Andy Turnpenny, managing director at Fawley Aquatic Research, formerly part of National Power until it was threatened with closure and the staff bought it out, said the system - which he described as the marine equivalent of a bird scarer - had been tried in the US but had to be repeated with European freshwater, estuarine and marine species.
The work will help power stations (the largest extractors of water in the United Kingdom), fish farms, irrigation schemes and the water industry in general. Mr Turnpenny said: 'We have been delighted with the results so far. The work being done has generated a lot of interest.'