Surface water that sinks into the sinkhole plain in areas near the intersection of Shiloh Road and Indiana State Road 135 south of Corydon has been observed to flow through known parts of Binkley's Cave, subterraneally under Indian Creek, exit to the surface at Harrison Spring, and flow to the Blue River. There may be a link under Indian Creek between Harrison Spring and Binkley's Cave. However the route would certainly involve many long cave dives – nothing of which on such a scale has ever been attempted in Indiana. Such a connection would likely greatly expand the known lengths of both caves as there are still significant gaps of unexplored cave in between the two systems. Binkley's currently measures around in length – the longest known cave in Indiana and the seventh longest cave known in the United States – and its known extent is increasing due to the efforts of the ISS. Cave divers led by Dave Strickland have mapped several thousand feet of cave in Harrison Spring – all of which was at a significant depth, and entirely underwater.