In lieu of actually seeing the object, you might try this. \n\nGet a length of rope and tie it to an anchor. Hold onto the free end of the rope and drop the anchor near the center of the area you want to search. Holding the rope swim away from the anchor until the rope is pulls tight. Swim in a circle around the anchor, along the bottom, at the end of the rope. If the object is sticking up and hasn't settled in the silt, the rope will snag. At that point, you follow it back to your target. \n\nI know of at least one case where this method was used to retrieve a snowmobile that had gone through the ice on a frozen lake.