These include Vienna (capital of Austria), Bratislava (capital of Slovakia), Budapest (capital of Hungary), Belgrade (capital of Serbia), and numerous other large municipalities. Historically, the Danube was an exceptionally important river to the Greeks and Romans.
At that age, kittens are eating on their own and going to the bathroom on their own, so they can be away from mom for a day while she gets fixed. If mom is feral, when the kittens are 5 weeks old, that is the point when you can get mom spayed and release her right where you trapped her. Kittens can be safely fixed as soon a they hit 2-3 lbs., which is generally between 8-12 weeks.
The good news is that once you're back on land, the condition eventually goes away. It usually doesn't happen immediately though -- most people experience brief lingering effects. These effects can last a few hours or a day or two. In these cases there's really nothing to worry about.