Riss Lake is one of the areas that I was streetviewing early on in this case, simply because it was a large body of water NW of QT and I saw from crimereports.com that drug dealing crimes occurred in that area often.
In terms of an accident, it looked unlikely to me that a car would be able to go over the guard rails on both roads that go parallel to the shoreline. I would think you'd see some kind of damage if that much force was generated to go over the rail and into the lake. Also, when ground is freezing or near freezing and wet, it's extremely easy for the grass to be damaged.
However near the southern road (NW Lakeview Dr) there is indeed a spot where I think someone could go off the road and into the water without hitting the rail at all, just drive right in.
So that's the spot I'd be checking first.
Does anyone know the exact location that the vehicle they found today was pulled out? was hoping there was another camera angle from further away at some point to give that context.