Why won't the mallards go in the water?
Mallards prefer still quiet water, but also spend a significant
amount of time sitting on the grass, or waddling around pecking at
food. If the mallards won't go in the water, look at water
temperature, water quality, flow rate, or presence of a predator.
Domestic ducks need a large bathtub sized water container for
swimming, but will avoid soiled and stagnant water.