Our sky is wide, a seeming huge flattened dome stretching out to infinity at its horizon extremities. Not so a fish’s, or a sea lion’s or an underwater swimmer’s. Their sky is a narrower wave ragged circle overhead on the water’s surface.
Light rays are refracted when they enter water to make a steeper angle to the surface. Rays entering the water after almost skimming parallel to its surface are refracted most and they descend at an angle of 49° to the vertical. The whole sky is compressed into a 98° wide circle.
The compression is not regular. If the water was ever still a fish would see objects near to the sky horizon somewhat squashed.