Can't Access Blight Cyst

I was able to access and get the rewards for the other two cysts but not the Blight Cyst, neither from the front or behind it. The little square pond with arches block it from the right, and the left is blocked from the shape of the map. My mouse can hover over it but when I click nothing happens. This is for the Strange Growths Quest (Act 3) with Cassia.