The invention provides a protective structure for a subsea installation. The protective structure comprises first and second body portions and a hinge member. The body portions are pivotally mounted to the hinge member such that at least one of the body portions may pivot relative to the other body portion. The body portions occupy a first configuration which facilitates transportation and/or deployment to the seabed and a second configuration in which the body portions are arranged to substantially enclose the subsea installation when the structure has been positioned over it. First and second locking means can lock the structure in the first and the second configuration respectively. Additionally the protective structure can allow access to the subsea installation when in use, by provision of a closable opening.