Something that might be interesting to look at on a similar vibe to this is apparently the Firth of Forth (Scotland) is meant to be radioactive as well (particularly around Dalgety Bay (Fife)) and its said that this is due to crashed Luftwaffe planes from WW2 (and their radioactive night-time instruments leaking into the water) - The increased radioactivity in the area was a main cause of concern when the MOD originaly wanted to decomission the Trident submarines in Rosyth marina as many people believed the decomissioning would further highten the levels