Thermals are forming behind the foot of a ridge line due to the eddy currents in the air mass. The swiliring air mass circles behind the foot, gathering in all of the hot air, and thermals rise near the center of the swirl. A good example of this may be seen using water rather air. While standing on a bridge over a large river, watch the water pass around the pylons supporting the bridge. You will see that the surface of the water is actually higher in the swirls as the water is forced upward.
Thermals form downwind of a lake.
This can happen if that area of the air mass is stratified. The cool surface lake air is channeled around an area of moderatley warm surface air, and as that surface air ascends into the cooler air well above the surface, it ascends rapidly in the form of a thermal. Such a thermal will be a cooler thermal than those not downwind of a lake. That is, it wouldn't have formed except for the localized area of cool air. Thermals form as the surface air is cooled due to a sea breeze, forcing the warm air aloft.