Thanks for all your advice, adventureadam.

My question was not intended to be a dig at you nor PRG, just precautionary.

Have been to PRG before and didn't notice anything unusual, but we didn't ride on any of the rivers (we did cross some bridges). Moreover, we went in November (colder weather).

I've also been to Manila, Hong Kong and Tokyo before where it is not unusual to wear a even a basic mask due to pollution. But there are also plenty of people who don't bother. I certainly haven't.

So once again, it was only just to clarify the extent of the situation - it wasn't a dig at you.