Yes and no. you can make it work by having a hard ground: Mercury is heavy. 13 times denser than water, so I would put it into a not too deep, flat lake with some kind of solid rock bottom. More importantly: Mercury is very much not reactive, and it does not corrode. So have no worries about it corroding away. Another problem is that it will evaporate. Very slowly, but it will. Not enough to have clouds and rain but too much for it to stay forever.
a drop evaporates at 6ng/h, surface area of a drop is 50mm^2. chiemsee has 1,5x10^12 times the surface area and thus evaporation rate: 9480kg or almost 10 tons per hour. (22046.2 pounds). That is only 667 liters or or 3.2536585e-8% of the total volume, but on it will take only 3073463268.37 hours, 350851 years or 0.0077% of earths total life.
I am not saying it is impossible, but the fumes would kill you all around it. Maybe life around it will adapt? Who knows.
EDIT: Unless it is sourrounded by huge mountains, water will rain onto it, will float on top of it and cover it. There won't be any evaporation, since it is completly covered. But there will also be nothing to be seen.
EDIT2: I forgot to mention that if there are no winds it will not evaporate as fast, as the evaporated Mercury will not be carried away, which hinders the evaporation rate