Can you swim in America in April?

Swimming is definitely possible at any time, because indoor swimming is generally at room temperature, and outdoor swimming depends on the weather in different regions.

Take April as an example:

In San Francisco and the west of Los Angeles, the climate is pleasant, estimated to be around 20 degrees, which is relatively dry.

The temperature in the east is similar now.

You'd better prepare two thick coats in the central mountainous area, because the temperature difference between morning and evening is large, and it will be below zero at night.