An underwater material moving device (10a, 10b; 110a, 110b; 210a, 210b; 310a, 310b; 410a, 410b) comprising: a body (20; 120; 220; 320; 420); an inlet (25; 125; 225; 325; 425) provided on or at an end of the body (20;125;225; 325;425); and an outlet (15; 115; 215; 315; 415) provided on or at another, opposite, end of the body to the inlet, wherein the body comprises a through-passage (21; 121; 221; 321; 421) extending from the inlet to the outlet, wherein the outlet is provided on an outlet portion comprising an inlet end (55; 155; 255; 355; 455) and an outlet end, the outlet end comprising the outlet of the device, the outlet portion comprising a first dimension, a second dimension and a third dimension, the first dimension being a width or breadth dimension of the outlet portion, the second dimension being a length dimension of the outlet portion, and the third dimension being a height dimension of the outlet portion which extends along a direction of a longitudinally extending axis of the body, the first dimension of the outlet portion decreases or tapers along at least a portion of the third dimension in a direction from the inlet end towards the outlet end of the outlet portion, and the outlet comprises an elongate shape or slot (16; 116; 216; 316; 416), the inlet and the outlet are substantially disposed along the longitudinally extending axis of the body such that the inlet and outlet are aligned with one another, characterized in that the device further comprises one or more primary or guide blades or vanes (375a; 475a), and each primary or guide blade or vane comprises a first curved portion and a second curved portion, the first curved portion being curved or bent in an opposite disposition or direction to the second curved portion. a body (20; 120; 220; 320; 420); an inlet (25; 125; 225; 325; 425) provided on or at an end of the body (20;125;225; 325;425); and an outlet (15; 115; 215; 315; 415) provided on or at another, opposite, end of the body to the inlet, wherein the body comprises a through-passage (21; 121; 221; 321; 421) extending from the inlet to the outlet, wherein the outlet is provided on an outlet portion comprising an inlet end (55; 155; 255; 355; 455) and an outlet end, the outlet end comprising the outlet of the device, the outlet portion comprising a first dimension, a second dimension and a third dimension, the first dimension being a width or breadth dimension of the outlet portion, the second dimension being a length dimension of the outlet portion, and the third dimension being a height dimension of the outlet portion which extends along a direction of a longitudinally extending axis of the body, the first dimension of the outlet portion decreases or tapers along at least a portion of the third dimension in a direction from the inlet end towards the outlet end of the outlet portion, and the outlet comprises an elongate shape or slot (16; 116; 216; 316; 416), the inlet and the outlet are substantially disposed along the longitudinally extending axis of the body such that the inlet and outlet are aligned with one another, characterized in that the device further comprises one or more primary or guide blades or vanes (375a; 475a), and each primary or guide blade or vane comprises a first curved portion and a second curved portion, the first curved portion being curved or bent in an opposite disposition or direction to the second curved portion.