The River Manifold flows underground from Wetton Mill, and rises again at Ilam in the grounds of the hall. At some times of the year, the river bed is completely dry apart from the occasional pool. The River Hamps is a tributary of the Manifold which also flows underground leaving a dry river bed. At Ilam Hall, the Manifold rises a few yards downstream from a local spring. During certain weather conditions, when muddy water flows upstream of Wetton Mill, there is a clear difference between the clear water from the spring, and the muddy water rising just downstream.