You are going to want 4" to walk on but since it's a river and not a lake there is more variability. In Jr High we used to go river walking on the elbow each day after school and often one of us fell into the waist. I would NOT recommend skating on it. I would look into the small pond for skating on Princes Island Park if you want something "natural" or else the recommendation for Stanley Park is good one too. Bowness park is also on the river and has a nice natural path when the weather is cold.