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
Use She swam the length of the dock.
Use She has swum the length of the dock.
Avoid She swum the length of the dock.