Access is difficult, and the fish are very concentrated into small areas, but some are quite sizable so it is worth the effort.
Being well versed in biology and geology, it doesn't surprise me when I come across these streams any more. They still fit the parameters that are required for brook trout survival. Their existence in these places is a little more tenuous, because all it takes is one idiot to dispose of waste into a storm drain and a huge population bottleneck occurs. These streams actually come and go, populations rising and falling dramatically in a non-cyclical pattern. The problem with a rapidly fluctuating population is that it increases the likelihood that it will eventually hit zero. So, though it isn't surprising that these suburban and urban streams do have wild brook trout, I am not shocked when I run into one that has died. These are the streams on the edge, they will be the next ones to slip away. These are the ones that we hurt when we take too long a shower in late summer. These are the ones that we hurt when we wash our cars in the driveway. These are the ones that we hurt when we dump four bags of lawn trimmings in the ravine. It doesn't take much effort to keep these streams habitable.