Most thermal power stations (including nuclear) have a circulating water (CW) system. If cooling towers are not used, then it is drawn from the sea, rivers or lakes and discharged out again. It is quite safe to bathe in those waters, indeed fish thrive in the warmth. There are strict controls affecting any chemical or radioactive discharges. I have been in the River Blackwater adjacent to the former Bradwell Power Station as have many others.<br>I have also bathed in Geothermal waters in New Zealand where there are warnings not to submerge ones head due to a biological hazard, but otherwise most enjoyable.