RedactedNarrative: On Tuesday August 29, 2017 at approximately 20:00 hrs, V1 was cruising through the ski zone at Green Valley State Park when he struck a submerged tree.  The submerged tree was part of a sunken brush pile that had been put into the water, for habitat restoration by the DNR.  The tree had come loose from the bundle of brush and drifted into the north end of the ski zone.  The tree was completely submerged yet part of the tree was within 1 to 2 feet of the surface and unable to be seen. While making the turn between the turn buoy and end of the ski zone buoys, V1 struck the tree with the lower unit of the outboard motor.  V1 estimated his speed as going  35 to 40 mph.  No injuries were reported with this incident.  Once the tree was located by DNR staff, it was towed out of the ski zone.  No individuals were wearing any life jackets.