In the context of Gormenghast, this intriguing river colour would unlikely be a sign of toxic effluent or bloom, so it struck me, along with the prediction of inheritance fishing.

‘The lime-green river where twelve years later he would be angling for the hideous fishes of his inheritance.’

Source: Mervyn Peake, Titus Groan (London: Vintage Books, 1998), p. 47