Apparently, the difference between a "Teich" and a "See" (masculine) in German is that a "Teich" is man-made.
That's not something I think I ever knew; I think I made a distinction more along the lines of English "pond" vs. "lake", i.e. purely by size rather than by origin.
I also didn't know that a "Tümpel" is characterised by drying out occasionally rather than carrying water all the time; for me, it was also merely a word for a small body of standing water. (And part of my passive vocabulary, at that.) Then there are also "Weiher", which is even less familiar a word to me.