First of all drowning is a horrible way to die but I will assume you know at least that much at this point.
I would imagine that lots of people die in rivers largely because of the strength of the currents, which make it difficult to stay above water even if they can swim.
I assume that is not the case for the average lake. So I guess you would have to make a judgement based on the lake and your swimming ability and figure out what to do to fight your inevitable survival instinct and make sure you stay underwater.