The lake froze overnight Dec 2-3 with 1" of solid ice, thick enough so the wind did not move it around and create pressure ridges. Since then there has only been a skiff of wind driven snow which left lots of visible ice between the drifts. 

The ice thickened with several more cold -20c (0f) nights. It got to 3" before a mild spell which had no effect on it. The ice is clear and appears black like the water below. I could see the cracks so I wouldn't trip in them, but more importantly so I could see that the ice was thick enough. 

My outbound segment was skated slowly with caution and vigilence to ensure the cracks revealed adequate thickness. Some areas were so smooth that, without the cracks, you would think it was still open water. Freaky. 

The ice thickness was consistently 4" or so, the minimum safe thickness. With the afternoon light failing and my confidence in the ice thickness improving, the return segment was skated in 9 minutes including a tour of the north shore.   

Got home and saw Peterborough firemen in a rescue exercise warning people to stay off the ice! True if there is any running water. Not the case where I was skating. I stayed away from the dam. 

Good thing I skated the lake when I did because a 3" snowfall covered the ice the next day. 

By the way, the ice continuously cracks and groans during the wide swings in temperature. If the crack is really close it is quite scary to hear even from inside the cottage. Imagine then, skating along and hearing a crack passing right under your feet as it progresses across the lake! As confident as I was about the ice thickness this was a pretty unnerving feeling.