Abstract: The invention pertains to a hydroelectric generating system for use with low-head dam and spillway installations. A vessel in the form of a barge contains ballast tanks, pumps and associated structure permitting the vessel to selectively float or to be submerged at a spillway. The vessel contains a plurality of horizontal penstock and draft tube passages extending therethrough each containing a turbine for generating electricity. The vessel is of such configuration as to be floated into the gate of a dam spillway wherein the water flowing therethrough passes through the vessel passages energizing the turbines to generate electricity. Anchor apparatus defined adjacent the spillway and complimentarily shaped abutments defined upon the vessel cooperate to maintain the submerged operative position.