[5][6][7] The upper reach of the river above the hamlet of Litton is known to dry up in the summer months with the water flowing underground.[8] It is known that there are huge caverns underneath Littondale where the water sinks, but it reappears south of Arncliffe.[10] The water seeping underground is what Marie Hartley and Joan Ingilby state is the reason that saved the valley of Littondale from becoming a huge reservoir.[11] Leeds council considered taking the waters from the river in the 1850s, which they labelled as the "Skirfare Scheme.Imported signal crayfish were kept in a trout farm on the Wharfe in 1983, and it is thought they have got into the river system from there.