Waterproof

I assume that was a typo and you meant a series 7 Apple Watch. Your Apple Watch is water resistant, but not waterproof. For example, you can wear and use your Apple Watch during activities such as exercise (exposure to sweat is OK), walking in rain, and washing your hands. For more info, see:

About Apple Watch water resistance - Apple Support

Apple Watch Series 2 and later can be used for shallow-water activities like swimming in a pool or ocean, but you shouldn't use models other than Apple Watch Ultra for diving, water skiing, or other activities involving submersion below shallow depth or high-velocity water.

Are you asking about iPhone or Apple Watch? This is the Apple Watch forum. If you are asking iPhone, no iPhone ever made is waterproof and NO, you should NOT swim with an iPhone. If you do, it will surely be destroyed and Apple will offer no service options to you.

Apple watch is water resistant, not waterproof and like iPhone, if it is damaged by swimming in salt water, which is more corrosive than fresh water, it will NOT be covered under warranty. The only watch I'd swim with is the newest Apple Watch Ultra, personally. It was designed with a higher water and dust resistance rating.

You can try swimming with Apple Watch, but given it won't be honored for warranty should it damaged, it's up to you if you want to risk having to buy a new watch.