During the Vancouver Island Transmission Reinforcement project carried out by the British Columbia Transmission Corporation (BCTC) in 2008, three old 138 kV HVDC underwater cables connecting the mainland to Vancouver Island were replaced with a new set of three single-phase 230 kV HVAC cables (outside diameter: 140 mm, weight in air: 61 kg per linear meter). The cables were laid on the seafloor in August–October 2008. The cables are self-contained fluid-filled, with paper-polypropylene insulation, lead shield, copper return conductors, and galvanized steel armour (B. Poirier, BC Hydro, pers. comm.). These cables traverse Galiano Ridge sponge reef (Fig. 1). Other human impacts in the reef area include occasional commercial prawn fishing (L. Barton, Fisheries and Oceans Canada, pers. comm.).