Normally those are roadbeds. Maybe there was a hiking trail or scenic walkway around there before the lake was created. It's the only explanation I have since the one is a about a perfect circle.
Roadbeds are marked as roadbeds as well as fences and creek channels.
This was farm/ranch land and these markings are are all over the lake.
Stump fields or standing timber?
Could it be a couple of old ponds that existed before the lake was flooded?
They may have missed the timber, stump fields and old ponds on these 2 as they are marked very clearly all over the rest of the map.
Oh well, Thanks all.
Modified by stogie at 9:35 PM 12/20/2011
they're not ponds. there's no depressions or dams. run over then with your sonar and see if they are harder than surroundings. my guess is dirt/gravel roads.
They should be clearings. Cleared fields or cleared open areas show up this way on topo maps. you will notice that there is flooded timber all around the area, but not in the hashed areas.