Rīga City Council has published a list of the nine public swimming places approved for use, ranging from lakes to rivers and even the shores of the Gulf of Rīga, all within Rīga city limits.
At present the list is only available in Latvian and Russian, but should be fairy easily understandable with the help of online translation, and include details of how to get to each location, what to expect when you arrive and other useful information, such as whether lifeguards are present, whether there are changing booths, etc.
You can find the full list at: https://www.riga.lv/lv/rigas-pilsetas-peldvietas#udens-temperaturas-riga and you can see videos of some of the locations on the Rīga municipal YouTube channel among the recent uploads.
While swimming outdoors is a wonderful experience, it's worth remembering that by most metrics, Latvia's drowning statistics are the worst in Europe, so please be sensible and stay safe!
And if you are in need of rehydration after all that exercise, you may like to refer to our recent story about water refill points in Rīga.