The PixelAttribibutesB_Casc RenderTargets contain the Foam value in the B channel. This value is calculated in the FoamAndExport stage of the WaterSim emitter. It is written to the RenderTarget in the ExportPixelCascade0 through ExportPixelCascade4 stages.
Your screenshot doesn’t necessarily look wrong for what you would expect to see for Cascade0. It depends on the foam parameter values.