GSF will ascend streams so small you could easily jump across them if not just step across them.
I think too much of a big deal is made when GSF are found in a pond. In a pond already established with BG and LMB, GSF quickly become outnumbered and within a few years are almost absent. Manage your BG and LMB correctly and the GSF will have little to any affect on your pond.
I have manged ponds that initially only had 1000's of GSF in them. Within 5 years are stocking LMB and BG, the GSF were rarely even seen anymore.
