The Mahaweli Water Security Investment Program (MWSIP) is the final step of Sri Lanka's Mahaweli Development Plan (MDP), a multi‐sector development of the water and land resources of the Mahaweli Ganga (River) Basin and North Central Province and Northern Province. The proposed contribution aims to provide a general description of the MWSIP and to focus on the tunnelling works of the programme. Water transfer tunnels have been designed along the alignment of the different projects of the MWSIP: The contribution will focus on the 26.6 km long tunnel of Contract UECPICB‐2A, which is the largest single investment of the programme, and will present the criteria and boundary conditions for the tunnel design, such as the geological and hydrogeological conditions, environmental considerations and in particular the impact on the groundwater regime and proposed mitigation measures. It will provide an update of the current status of execution and elaborate on the main challenges during construction.