A wellhead assembly and a method of installing a wellhead assembly. The method includes providing a well casing; providing a wellhead support structure; locating and fixing the well casing in a hole in the waterbed, wherein when the well casing is located and fixed in the hole the wellhead support structure is located a distance above the waterbed so as to leave a gap between the surface of the waterbed and the underside of the wellhead support structure; and fixing the wellhead support structure onto the surface of a waterbed with a settable material by putting the settable material into the gap when in a non-solid state to provide a rigid connection between the waterbed and the underside of the wellhead support structure. The assembly is arranged so that bending moments applied to the wellhead assembly can be at least partially transferred to the waterbed via the wellhead support structure.