My Watermark is the Ottawa River, Ontario.
In July, 1998 my family took me to the Ottawa River where the Mississippi River meets Marshall Bay. We were on the 20 foot long, Micmac cedar strip canoe (a David Hazen design, as featured proudly here: http://www.craigmarine.info/yacht_boat/builders/canoe_boat/Handcrafted-Custom-built-artKayaks.htm ) that my dad had handcrafted in the years before.
I was only 4 at the time but I can still remember gliding along the sparkling blue green water, and how cool it was despite the warmth of the mid-summer. It was so serene and perfect, that the memory is like a postcard in my mind and I wish we had taken the Micmac on the water more often as a family.