Geographically that lake is unlikely. If all the small tributaries are flowing from that point then its probably the highest point on the map or at very least it definitely is on the watersheds of all the rivers. Lakes don't form on the watersheds. You do occasionally have lakes high up in mountainous regions but the rock would have to be impermeable like granite. But these are usually in the basin of even higher regions as water collects into them.
I always find it much easier to get the height of an area first and then determine water flow based on guessed watersheds and then where a lot of water is naturally collecting and the ground is flat is where lakes go. If you are going to apply some hill graphics and mountain symbols then its going to be interesting to see what you do at that point.
Perhaps a caldera might be an option tho ?