Question

Why do bodies of water tend to moderate temperature swings from day to day?

Answer 1

The bodies of water tend to have moderate temperature swings because of the high heat capacity of water. The heat capacity is the ability of a substance to retain heat energy. The water in seas and oceans become warm during the day time, but take time to loose heat in the night. This  gradual loss of heat energy maintains a moderate temperature around the shoreline.

Answer 2

Because water has high heat capacity