The odd thing is that it's shape looks more like a domestic cat. It's not lean like a mountain lion, although it is hunched up in the photo. Compared to that chair, though, it's the size of a young mountain lion at the shoulder.
I don't have a CAD program on the home computer to mess around with that photo ... but I tried putting lines on the chair to the left of the kitty, moving them to the cat, and assuming the cat's about 14 feet from the camera and the chair about 3 feet from the cat's rear, and using the O.P.s chair measurements ..
I'd guess about 20"-22" at the shoulder. Looks almost 4' long in the body to me, maybe 5' including tail, though it's hunched up in the photo, so hard to tell. If those are close guesses, then about 50 lbs or so. Not a domestic cat, unless I' way, way off and fooled by the camera perspective.
Hard to tell from one nightime photo, distance to the camera can be deciving ... but I'll still say that's a juvenile moutain lion, and the colors are washed out from the camera.
Try putting some stakes in the ground so they're 2' tall, near the water and in frame, and compare in the next shot. Put some white tape at the top of the stake. If it's 2' at the shoulder or so, it's a mountain lion, not a domestic cat. If it's a bit shorter, it's a young one.