swim / swam / swum
The past and the past participle of swim.
The past of swim is swam. The past participle is swum, after forms of have and forms of be: He swam. He has swum. The channel was swum. Do not use He swum for the simple past.
Examples
UseShe swam the length of the dock.
UseShe has swum the length of the dock.
AvoidShe swum the length of the dock.