The creek I was in is certainly nowhere near those depths. Most of the creek seems to average about 3 - 4' at high water with the two deepest holes I've found so far around maybe 8 - 10'.

The perch that are in the coastal bay creeks are essentially stuck up in the creeks though due to intolerable salinity levels further down the system where the creeks meet the back bays. I've never heard of perch being caught in the back bays.