Abstract: This invention relates to a submersible hydroelectric generator apparatus (1) and a method of evacuating water from such an apparatus. The method of evacuating water from a submersible hydroelectric generator apparatus (1) comprising the steps of pressurizing a fluid supply in the submersible hydroelectric generator apparatus using the water flowing into the apparatus and thereafter using the thus-pressurized fluid supply to evacuate the water from the apparatus. Additional pressurized fluid can be supplied to provide a pressurized fluid supply with sufficient pressure to expel the water from the apparatus. The apparatus (1) can be used in a grid connected electricity generating system or indeed in a smaller scale implementation such as in a single building or group of buildings to provide electricity to those buildings. The invention overcomes problems with prior art devices by evacuating water from the apparatus in an efficient manner.