Generally, using digital zoom can decrease image quality because it essentially crops and enlarges a portion of the image, which can result in a loss of detail and sharpness. However, some of the newer waterproof digital cameras have advanced image processing algorithms that can mitigate this quality loss to some extent. If image quality is crucial for your shots, it's recommended to use optical zoom when available or get closer to your subject if possible. Always review the camera specifications for details about its zoom capabilities.