Inspection Pit Recovery

We have never seen the bottom of our inspection pit. It has been full of water since before we moved. Was it the state of the garage roof? Is it groundwater? Is it the juices of a thousand decaying mice? I have no idea. Perhaps it is all of the above. But I dread finding out what is the bottom.

You can see some planks of wood floating on the water. That's where N almost fell into the black soup.