The emissary entrance is a few metres above the current level of the lake, on the south-western shore. An 18th century portal gives access to a first stretch of tunnel clad with large opus quadratum blocks for about 25 m. A stone plate with circular holes, part of which is still in situ, was a filter to prevent entry of logs and other large debris. Grooves in the walls are clearly visible for bulkheads which could control the flow of water and allowing the filters to be cleaned. The original plan was for the entrance to be on the same level as the floor of the main tunnel but there is a steep slope from the outside to avoid water entering the tunnel while under construction. The entrance floor was to be lowered once completed but this was never done.
The emissary entrance is a few metres above the current level of the lake, on the south-western shore. An 18th century portal gives access to a first stretch of tunnel clad with large opus quadratum blocks for about 25 m. A stone plate with circular holes, part of which is still in situ, was a filter to prevent entry of logs and other large debris Grooves in the walls are clearly visible for bulkheads which could control the flow of water and allowing the filters to be cleaned. The original plan was for the entrance to be on the same level as the floor of the main tunnel but there is a steep slope from the outside to avoid water entering the tunnel while under construction. The entrance floor was to be lowered once completed but this was never done.