I believe the rock your asking about is actually Rigney Rock. It's located about 1000' off shore from the Dewey Ave. / Lakeshore Dr. intersection in about 12' -15' of water. The rock your calling Turtle Rock is located off of the East side of Summerville off the point. Neither rock has a buoy as no one wants to take responsibility for them. Once the USCG marks an obstruction they now have ownership of it so , they don't mark them. In most cases, you will never have to contend with either of these rocks unless your trolling in very close in the spring or water skiing in the summer. Other than that you should be farther off-shore with your vessel. On the other hand, if your looking to fish around that rock for bass you can't miss it. As long as the water has some clearity to it you will see it all the time. I used to use it a jet ski turn in days past and it is no problem to spot. I am sorry I don't have lat/lon for it but I did get you VERY close to where you can find it. Doug