ORCA (Oscillation Research with Cosmics in the Abyss) is the low-energy branch of KM3NeT [1], the next-generation neutrino Cherenkov detector currently being built in the Mediterranean Sea with the aim of measuring the neutrino mass ordering and searching for high-energy cosmic neutrino sources. The ORCA detector will consist of a network of 115 vertical strings supporting optical modules, anchored on the seabed off the shore of Toulon, France (see figure right).