Non-reference underwater image quality refers to the visual fidelity, clarity, and perceptual condition of an underwater image evaluated without comparing it to a distortion-free ground-truth reference image. In real-world aquatic imaging and marine robotics, obtaining an ideal pristine reference is generally impossible due to severe optical distortions caused by wavelength-dependent light absorption, scattering, color casting, and turbidity. As a result, non-reference quality evaluation relies on analyzing the intrinsic statistical characteristics of the degraded image itself, such as measures of sharpness, colorfulness, contrast, and structural information, or on deep learning models trained to score visual quality and gauge the success of underwater image restoration and enhancement algorithms.