An underwater trenching apparatus comprises at least one trenching tool; a lifting attachment point configured for attachment of a lifting means for lowering the trenching apparatus to, or raising the trenching apparatus from, its location of operation; at least two steerable endless track units for transmitting tractive effort to move the underwater trenching apparatus in use; and for each steerable endless track unit, a first mounting arrangement permitting rotation of the track unit about a vertical axis, and a first actuator configured to move the track unit about the vertical axis, and control means configured to control the action of the actuator. In alternative forms, in addition to, or alternative to the steerable endless track units, the apparatus includes height adjustment means for adjusting the vertical spacing between the main body portion and the respective endless tracks; and control means configured to control the action of the height adjustment means.