If you don't plan on keeping what you catch the slough isn't bad fishing at all, I've caught catfish just about any time of day as well as at night, I've caught a few bluegill and a yellow perch but most of the bites are cats, I've seen some carp, but never caught one. All I've ever used are night crawlers. Bank access can be tricky, the slough is lined with a lot of brush, I hope to get a Kayak next spring and get to some of the better spots, but for bank fishing under the I-205 bridge is pretty accessible. There's a path that runs (interrupted) from blue lake to somewhere past the airport, there are a few spots you can get close enough to cast along that path.
Standard disclaimer is that you need to read and understand the ODFW warnings before eating fish from the Columbia Slough. They're not the healthiest fish in the valley to be eating.