The Major causes for the underwater images are light scattering and color change. One of the methods of improving quality of the image is image enhancement. This paper presents a comparative study of various image enhancement techniques used for enhancing under water images. The quality of underwater images is poor because of specific propagation properties of light in water. When capture such images degrade due to many factors like ripples in water, lack of availability of light organic matter dissolved in water etc. and also such images are captured from very small distance so the images must be preprocessed before applying any kind of operation on these images different filtering techniques are available in the literature for preprocessing of under images. The filters used normally improve the image quality, suppress the noise preserve the edge in an image, enhance and smooth the image.