My Watermark is the Toronto Harbour of Lake Ontario.
As a triathlete, there is no substitute for open water swimming when preparing for a race. All the training hours in the pool over the winter come together that first time I jump in the water in the spring.
In the early months, a wetsuit is required, but come July/August it's warm enough to shed the neoprene. As much as I love a quiet lake up north, I have a special affinity for swimming in Lake Ontario right in my backyard with the booming metropolis of Toronto on its shore.