290 acre Redman discharges directly into 220 acre Lake Williams, so those who introduced the fish got a two for one with this introduction. Williams discharges to the East Branch Codorus, which then flows into the S Br Codorus about a mile downstream. The South Branch flows into Codorus Ck upstream from West York. The Codorus flows into the Susquehanna roughly half way between York Haven Dam and Rt 30.
There is really no need to talk about the snakeheads eventually ascending the Safe Harbor fish lift once past Holtwood Dam because over time they will probably work their way down from Redman and Williams to the Susky and the impoundment formed by Safe Harbor Dam, known as Lake Clark. They will also work their way upstream to York Haven Dam over time and that dam has a fishway(fish ladder). Then it’s a clear shot to Harrisburg once they work their way through the impoundment formed by York Haven Dam. Now it can be seen that when short-sighted individuals introduce an exotic an entire system of inland waters has the potential to get screwed up.
In the other directions, if they ascend the East Br Codorus from Redman, they are in a stocked trout stream and farther upstream a combined stocked and wild trout stream. I really doubt that they will be attracted by that cold water where the wild trout are located, plus the physical habitat is wrong. The same scenario exists heading upstream on the S Br Codorus except that they would first pass through a warmwater stretch. Heading upstream on the main Codorus would be tougher because of some dams.