Hi johnnyw the true part could be "real" the fish could be "garfish" giving you "reagar" dont know if this is right but im sure i will be corrected if not.dont know about the hot mineral spring part though.
Jonny - 'Realgar' is defined as 'a rare soft orange mineral consisting of arsenic sulphide; an important ore of arsenic'. It is found in hot spring deposits and of course 'gar' is the fish, so all words are accounted for! Good Luck! ja