I'm thinking about a local ditch, similar to what you describe. One side is nearly vertical, the other side is fairly steep, but if you watch your step you can walk it.
If the ditch was just dredged, a year or 2 ago, has it had time to be sodded over yet? If there's no grass and weeds, you may not have as many rats as you think?
I believe I'd rip a hole in the dam, a foot and a half or 2 feet deep. With that much water, it'll take a day or 2 for the water level to even out. At least then you'd be able to walk the ditch bank, and check for tracks.
I'll tell you I really like to set on floating logs, boards work good too. If you can get your hands on a couple of old pallets, you'd have all the lumber you'd need.
If the place is infested with rats, it might be worth the time/effort to build a few platforms. And don't forget about the beaver.