As for Natrix natrix, I see them pretty frequently around here. A few years ago I even found a baby under a stone along with a slow-worm (legless lizard, even more common); today I would probably grab this baby and run like crazy to make a viv. They are protected species, BTW., just as every amphibian or reptile in Poland. Though I would happily keep a male (females are too big for my taste) - they are very common and I can't imagine how taking one male would harm natural enviroment. Oh well, I have criminal thoughts.

Never saw a smooth snake nor adder though, but according to sources, they do occur in my area; smooth snakes eat lizards and, like I said, there's plenty of legless lizards and sand lizards around here. I wouldn't take one though, unless I find out there's a big population around (which I doubt), not to mention problems with food supply.