IPA: /ˈlaɪfˌɡɑrdɪd/
KK: /ˈlaɪfˌɡɑrdɪd/
Supervised by a person who is trained to save lives at beaches or pools.
The lifeguarded area of the beach is safe for swimming.
Lifeguarded → It is formed from "life" (from Old English "līf", meaning existence or living) and "guard" (from Old French "guarder", meaning to keep safe or protect) and the suffix "-ed" (indicating a past action). The word "lifeguarded" means having been protected or watched over in terms of safety related to life, especially in aquatic environments.
Think of someone who is 'keeping safe' ('guard') those who are 'alive' ('life') — that's why lifeguarded means having been protected in a situation involving water.
No commonly confused words.