Since most of such types were terrible swimmers, my theoretical solution was to grab the mugger, drag the both of us into a deep spot, if close by, and drown him. Other than that, I’d jump into the lake and challenge him to follow me in the hope I’d be able to grab him and drown him. If that was your plan I hope you kept a close eye on Lake Temperature.
A good portion of the year you would probably kill both of you from hypothermia.