I completely forgot about a slab of ash I had stored on the floor and it looks like water has seeped into the edge. It was stored horizontally on an edge, leaning against the wall. The edge against the floor is the area of the stain.
It's a rough sawn, live edge slab that hasn't had the bark removed or been through the planer yet. Will the water damage be removed with sanding, something else or is the stain there for good?