Yes, upstream of Wanapum to Rock Island the shoreline is closed due to the reason you list above. I would imagine the pool will remain low for most of the summer. Above Rock Island and below Wanapum the shore line is open.
My Dad and I found arrowheads in the sand there back in the '50's before flooding occurred from the damming of the river.
I was just a little kid, but I still remember the heat of a summer day on what was once a very large sand bar on a glaringly hot day with no shade.