Hmmm...there's the KOA of course. And then some camping up above Roslyn. But I would watch the flows.
http://waterdata.usgs.gov/wa/nwis/uv/?site_no=12484500&PARAmeter_cd=00060,00065
http://waterdata.usgs.gov/wa/nwis/uv/?site_no=12484500&PARAmeter_cd=00060,00065