I lost a pair of $600 specs overboard near my mooring, in Gosford at the time. Deoth about 3m and mud bottom. I mentioned it some weeks later to a friend who was an ex navy diver. "No worries mate we'll find them".
He brought up his diving gear the next weekend (lured by a carton of free beer) and rolled into the water with a length of flouro line attached to himself and after diving below the other end tied to my mooring block.
Then he swam slowly in diminishing circles and let the flouro line pull him a tiny bit closer to the mooring block as it would around it and as he swam round and round. We sat on the boat watching the bubbles circling the boat.
Suddenly up he came from the depths with huge grin holding the $600 glasses. He said he had to swim around 6" off the bottom to see what was tuhere because ir was so murky and very slowly not to stir up the dust and they were half under the mud and given another month or two we wouldn't have found them. Amazing