Will it be okay for me to go to the beach/swim in the sea one week after my microdermabrasion treatment?

The only concern when going to the beach one week post-treatment would be prolonged exposure to UV rays. Take all of the standard precautions such as sunblock, a wide brimmed hat, and sunglasses and you should be fine.

Microdermabrasion is a very superficial treatment of the skin. The skin usually heals within a few days after treatment. It is recommended to avoid the sun or use sun block for the first few days after microdermabrasion. You should be able to enjoy the beach or similar activities one week after treatment. 
Remember, always use sun block to avoid skin cancer. But as far as your microdermabrasion treatment is concerned, one week is plenty of time for your skin to completely heal.
Good Luck!

Use plenty of sunscreen and you should be fine, especially a week later. For future reference, wait at least 1-2 days afer a microdermabrasion treatment before exposing your face to UV rays.

I agree with your decision to wear sunscreen and a hat. It is a good idea no matter what. There should be no problem being outside or swimming a week after a microdermabrasion treatment. In fact you are probably OK the day after.

I agree with all the precautions mentioned including hat, wide spectrum UV protection, SPF 30+ and I recommend Spectrase. I also recommend an Opti-Ceramide cream for deep moisturization and hydration of the skin.H Karamanoukian MD FACS

I recommend that patients avoid excess sun exposure for about 24 hours after a microdermabrasion.  Beyond 24 hours, as long as you use a good sunblock (make sure to use one that is a physical block, not just a chemical block) and remember to reapply frequently, you should not have any problems.Enjoy the beach!

Microdermabrasion is very superficial and activities do not need to be curtailed at all especially after a week

Thank you for your question.
Yes, provided you have and continue to use the precautionary methods of sun protection that you have listed (ie sunblock, hat, etc), then you are safe to go to the beach 1 week after your treatment (provided there are no other contraindications - eg. photosensitizing medications, etc)
Please consult with an appropriately trained and experienced practitioner to ensure your safety and for optimal results to be achieved.
Best wishes.

The only reason to avoid the beach one week after a microdermabrasion would be that you may be undermining your results by exposing your skin to UV radiation.  So if you take all possible precautions;  large brim hat, big sunglasses with 100% UV protection, wear sun block (UVA/UVB) of at least SPF 30 and re-apply after swimming and every hour regardless, you would be doing everything reasonable to protect yourself AND enjoy summertime activities.  And it's always fun to read a summer novel under the umbrella.  Have fun!