What factor can significantly change visibility underwater?

The bottom surface composition plays a crucial role in determining underwater visibility. Different materials found on the seafloor can reflect or absorb light differently. For instance, sandy bottoms often allow for better light penetration and clearer visibility compared to rocky or muddy surfaces, which may stir up sediments when disturbed, clouding the water. Additionally, if the bottom is covered in dark or uneven materials, it can create shadows and block light, further impacting how far you can see underwater.

Other factors like depth, presence of other divers, and time of day can influence visibility but are not as significant as the composition of the bottom surface. For example, while depth does affect light availability, it does not change the clarity of the water itself in the same way that bottom composition does. Similarly, while other divers can create bubbles and disturbances, the sediment or type of bottom material has a more direct and pronounced impact on visibility. Lastly, although the time of day can influence light levels, it does not alter the inherent clarity of the water affected by bottom materials.