A lake can have underwater reeds that can tangle a swimmer's legs. Be sure that the environment is safe before permitting any swimmers to go in. None of these environments should be used for diving. Swimming should be prohibited in areas where fishing and boating occur. The discussion above regarding floatation devices holds true here, as well.
Scuba diving has particular hazards related to depressurization.
Lessons and certification before attempting scuba are imperative. Any child with these problems must check with their physician before attempting this activity. Children with allergies may have trouble equalizing the pressure in their ears. They should also check with their doctor before engaging in this activity. Swimming exercises all of the body's muscles in a non-weight bearing way.