large black triangular shape had three lights red, white and blue, hovered a few minutes, no sound...

On July 29, 1987, I saw a UFO at Pigeon Lake (Ma-me-o Beach), Alberta, Canada.  The sky was clear with no wind.
My family (husband, daughter, daughter’s friend, mother-in-law, brother-in-law, brother’s friend and I) were vacationing at Ma-Me-O Beach.  We had a cabin on the beach with a firepit in the yard.  About 1:30 AM, my husband, his brother, his brother’s friend and I were sitting around the firepit talking.  Suddenly my brother-in-law said, "Look at that!," and pointed up in the sky.
Over the lake, at very high altitude, was a large black triangular shape silhouetted against the sky.  It had three lights at the widest point of the triangle, red, white and blue.  They did not blink.  At the speed of a regular plane it went to the middle of the lake, stopped and hovered for what seemed like a few minutes.  It raised itself up and down, and then took off at an incredibly high rate of speed.  It disappeared in a second or two.
We talked about it, trying to decide what it was.  My husband is well read on aircraft, and couldn’t match it to any he knew.  Years later we thought it might have been a Stealth bomber on a test run, but the light configuration, manoeuvrability and speed did not match.  Also, what we saw was much larger.
I have never forgotten the incident, and it remains clear in my mind to this day.  I still wonder what it was.