In Mines Quarries and Murders in the Peak District by Roger Flindall (PDMHS Mining History Special Edition, Vol. 16 No.1, 2005), the possibility of a hoax being perpetrated either on Lloyd by miners, or by Lloyd himself is raised - namely that the underground river never existed, and it was a wild exaggeration intended to add more 'thrills to the ride', as it were. I have no more idea on the veracity of that rumour than of the original tale, but it seems like a good place for a dig anyway, given where it is. And the fact that Windle and Rush mines, just up the hill, went down 660 feet to an underground streamway, presumably the P8 water on its way to Speedwell.
But digging a better tunnel through to the Main Chamber would seem to me to be the minimum required as it's disgusting and a serious health hazard in every respect at the moment.