Natural England via Professor John Gunn’s extensive (at least 10 years) experiments are stating that water which would naturally run down the River Lathkill is flowing down the Wye via Magpie Sough. Lathkill Dale Sough is only responsible for removing perennial flow from the river bed through Palmaston Wood, where Batemans House is, but all of the water returns to the river via The Bubble Springs.
Once water enters Lathkill Dale, it is only lost to the river for a short time. Magpie Sough is taking water from the river completely. Wheeldon found it, Banks found it and Gunn found more recently so it cannot be denied. Estimates revolve around the figure of 52% of Q95.
Magpie is responsible for removing the Lathkills natural entitlement and the Lathkill and its inhabitants are in serious need of that water, from the native crayfish to the kingfishers; from the trout to otters. For those who visit the cave occasionally and spend a couple of hours or so exploring, you might like to consider the River being without the water all of the time, with its associated problems relating to lack of flow.
To answer an earlier question, the fishery was operating when a famous angler called Isaak Walton recorded catching red trout in the Lathkill back in 1670. Did the photo you mentioned show a couple of men sat bolt upright with tea, some fish laid out in front and the fishing family more relaxed? The bailiff on the right (Bartram) is buried at Over Haddon.
Any possible project to return the Lathkills rightful entitlement of water could only take place before water starts to fall to the Wye, directing it back to its home in the Lathkill. The rest of the sough would be free to explore as it is now, just with less water, just like Hill Carr.
Thanks for listening.