The water quality is not great. Sewage often overflows after heavy rain directly into the water at Portobello. So avoid swallowing it and have a shower as soon as possible afterwards. A list of all the sewage pipes going into the sea is shown here: https://forthriverstrust.org/sewage-outfalls-around-the-firth-of-forth/
Swim shoes are recommended as there have been cases of people standing on weever fish. Also, watch out for the jellyfish in the summer.
Edinburgh Skinny Dipping Stories facebook group: https://www.facebook.com/groups/skinnyswimmers