Modern Nikon cameras are packed with optical elements, electronic controls and small mechanical components in a very small space. All these can be damaged by sand or grit finding its way into the camera’s interior. Most consumer cameras are not protected against dust or sand entering the camera body. Because of the number of holes required in the cameras body for inserting batteries, memory cards, USB connections etc and in most cases the movement of the zoom lens, complete sealing of the camera is not possible without having a major impact on the cost.

Sand in the mechanism of a lens
If sand or grit enters a camera it can cause various malfunctions, for example by blocking gear units for zooming, focusing or aperture control. Sand damage is not covered by the warranty. Repairs are usually costly because they include complete dismantling of the camera, thorough cleaning of all parts and extended adjustment work after re-assembly.
Please protect your camera against sand – including wind-borne sand. Regularly clean your camera bag/case's interior, as sand in the camera's case may get into the camera as well.