answered about 9 months ago by alpha
You're probably seeing the Vietnamese National Team training. They have a training center on Lac Long Quan street where many of the younger members live. They'll be out on the lake every morning (or so it seemed when I used to live down the road from them). In the evenings, you'll occasionally see them on the lake again or jogging in groups around West Lake. It's possible that there are other rowing club activities going on through this center as well, but I never saw any sign of them myself.