there are 2 dams above gateway park. The first dam can be seen by parking at the top of gateway park and looking downstream into gateway park on the upstream side of the bend. This same dam is a day wrecker, lots of wood, backwash and a definite portage.
The second dam is roadside upstream of gateway park, it is obvious and you will see it driving up in a river bend on your right. Portage river left.
If you started at the bridges take out you will have 1 low bridge, no problem.
and 2 dams, portage left on the roller dam, and when you get to the gateway park dam it is best to portage up to the road on river right and walk into gateway park to put back on.
The dam in gateway is sketchy, its best to stay away, and the river as mentioned above is scattered wide and shallow, it is not that worth while.
good luck, and have fun.