SPY has rallied exceptionally fast since bottoming out in mid to late April, gaining nearly $60 in ~2 months. However, this rally is not supported by volume whatsoever. We have had some of the lowest volume in history on SPY since May.
You can see that volume has been falling off of a cliff and is near the lowest levels in decades. There's been a steady decline in volume since the major bottom in 2009. This is a big reason why I believe we are nearing the end of a 15 year accumulation and distribution cycle.