The only way you're going to get an update of Temagami is to map it yourself. Last time it was surveyed was probably 1903 with two drunks in a row boat with 200 feet of rope and a rock.They found three common depths and drew a 140' depth circle, too bad they missed the 8 FOW tower in the center of the circle. You can drive your boat along shore on GPS and it'll show you're 100' in the bush on the South side and can't get to shore on the screen on the North !
BTW, if you need to use a cell it will work standing on the "Bell Beavers" lodge at the bottom of the portage into Browns Lake from Ferguson Bay. Even my flip phone will work there...