An axial flow turbine for generating electricity in low-head environments comprises a runner supported by guide vanes that are curved or contoured to direct flowing water onto fixed turbine blades. The axial flow turbine has a housing that provides an outer draft tube. A second inner draft tube is supported within the outer draft. The axial flow turbine may have a bulb or pit-type housing at the intake chamber for housing a direct-drive variable-speed permanent magnet synchronous generator (PMSG) and power converter system. The axial flow turbine may be installed as a single modular unit in low head environments.