Abstract: A blade (300) for a rowing oar (100), comprises: a first lifting element (310a) having a first chord line (320a) at a first point along its span, the first chord line extending from a trailing edge (340a) to a leading edge (330a) of the first lifting element; a second lifting element (310b) having a second chord line (320b) at a second point along its span, the second chord line extending from a trailing edge (340b) to a leading edge (330b) of the second lifting element; and a slot (370a) through which water may flow when in use, the slot (370a) having a constant width across more than half of the slot's length. The constant width extends between the trailing edge of the second lifting element (340b) and the nearest point on the first lifting element. The first and the second chord lines (340a, 340b) are non-parallel so as to form a first angle (550b) therebetween.