The only estuary that you can put a power boat in is the umtuvuma river. Launch at the old pont.
If you head up river you can target perch and rock snapper and other bits and pieces.
Top water lure against structure works well for the perch, a nice piece of sardine works well for the rock snapper.
If you head to mpenjati you can get some small kingys and grunter, but no power boats allowed there.