In some cases the shock itself is fatal, since the person will suffocate when their diaphragm is paralyzed, while in others it incapacitates the swimmer causing them to drown.
Electric shock drownings occur most often in fresh water, which is conductive due to dissolved minerals and impurities.
By law, all connections near water are required to have working ground fault circuit interruption technology, GFCI.
Faulty hydroelectric generators or damaged underwater power lines can cause leakage currents, potentially creating a hazard.
In general, anything electrically active that comes in contact with water has the potential to create leakage currents and contribute to this type of safety hazard.
It is common for faults to be tied to appliances or circuits that come on intermittently, meaning that the condition of the water can change instantly and unpredictably.
If the swimmers notice any unusual tingling feeling or symptoms of electrical shock, it is highly likely that stray currents exist and everyone needs to get out.
For cases where swimmers can feel mild tingling, getting flotation devices out to them can aid them to swim away from the current source under their own power.