A power generation apparatus for generating power from water flows is described. The power generation apparatus includes: a generator; a first blade set operatively mounted to the generator for rotation in a selected direction in response to flowing water from a selected direction; a second blade set operatively mounted to the generator for rotation and operatively connected to the first blade set, the second blade set being disposed coaxially with, and downstream of or in a wake zone of, the first blade set; wherein the generator is adapted to be driven by at least one of the blade sets, the generator being disposed generally coaxially between the first and second blade sets.