Let's say humans artificially create a lake of this size in Russia (or any other country). There are no rivers feeding into this lake. The only water supply that gets into it is rain collected into it.

How long would it take for a sizeable organism to appear there? Things like bacteria and phytoplankton and stuff like that would easily get into the lake by runoff. But what about things like fish? How long would it take for fish to suddenly appear there? And how long would it take for a sizeable population to develop there?