the temp you want to limit yourself fishing for brook trout at to not cause excess mortality on brook trout is 64 degrees due to research showing increased blood cortisol and migration to refuge at that level. The handful of brook trout streams I am aware of in Lancaster county are not going to support that temp. Also if it is 64 in the AM and you catch that fish it will have ti deal with the additional stress from being caught when midday temps hit 68-70 post release. My advise would be to just fo to Big spring in newville for brookies or go to litiz run for wild invasive brown trout and rainbows that you can fish for up to 67 degrees. If you really want a small stream brook trout experience your best bet is going to be second half of September if there is water and temps improve. Brook trout generally don’t start spawning in September. There are many people on here finding lower temps in brook trout streams but their deff outside of lancaster county and are often hemlock lined with excellent canopy thermal protect and coller at higher elevation than lancaster creeks.