Every stretch of water a boat can reach from New York Harbor without once being lifted out: the Hudson, the four state canals, three great lakes and the St. Lawrence. The color is how high the water sits.
No map of lake levels went into this. The Canal Corporation publishes every lock's lift and which way it lifts. Cut the channel at each lock and it falls into pools of level water; start at sea level in the harbor and add up the lifts, and every pool gets a height.
You can sail a loop without turning around: up the Hudson, west on the Erie, down the Oswego Canal to Lake Ontario, down the St. Lawrence to Sorel, up the Richelieu to Lake Champlain, and back down the Champlain Canal. The dashed labels mark the ways out.
The grey lakes are the ones you can't get to. Lake George, Canandaigua, Keuka and Skaneateles all drain toward the system, but over dams and falls, with no lock to carry a boat down.