The upper Savage mainstem gets quite warm in the summer in some areas. MD DNR did a study of brook trout migration in the watershed and found that brook trout vacate large sections of the main stem during the summer months and water temperatures reached well above 70 degrees in those areas. Places where you can catch 10-12" brookies in April don't have any brookies in the summer. If I am remembering the study correctly, some of those fish moved as far as 12 miles.
Before the C&R brook trout regs were instated on the Upper Savage, a lot of those larger migratory fish were being harvested along with the stocked rainbows. The brook trout population was being suppressed not just in the main stem but the tribs as well. Every year since those regs began has set a new record for brook trout biomass at many of the annual sampling sites. It shows the importance of those larger adults in the system and making sure they have clear access to tributaries.
I visited it in late summer a few years ago and the main stem near Poplar Lick was barely flowing, I didn't see any brookies there. Tributaries such as Bear Pen Run were just a series of puddles although they had plenty of trout darting around. Way up in the headwaters the main stem looked better and I saw a lot of brook trout. It could/probably does have a lot of spring influence in the far headwaters but I don't think it is enough to keep the entire watershed flowing strong and cool through the summer.
On that trip I didn't land any brookies in the Savage watershed but fishing was good in two other streams: a small creek that is actually a bottom release tailwater flowing through a gap in a ridge, and another stream that has cold mine discharge. All this to say that year round brook trout fishing in MD is the exception, even the most popular places have a down period of a few months where temps and flows aren't favorable for C&R fishing.