Swimming should never be a solo activity. No matter how well you swim, swimming alone is dangerous.
Inexperienced or weak swimmers, of course, must have company and/or supervision to be safe in and around water.
But even strong swimmers can encounter dangers in the water. They can get sick or have a cramp that makes it impossible for them to swim. They can get tangled in underwater weeds or other hazards. They can underestimate their strength and swim too far from shore or the pool’s edge. If no one else is around, things can turn deadly very quickly.
This means it is important to always swim in a group of two or more so every swimmer will have someone nearby who can help in case of an emergency.