Tool-tip says, I have enough naval combat units to blockade this zone, Long Island sound in this case. Didn't we have an icon indicating blockade. Black Dick's been out here three months, no icon showing blockade is on. Very strong Continental army in New Haven so I figured I would blockade the port. Doing something wrong am I?
Maybe the icon is hiding behind something else in that region.
Also, hold mouse pointer over the port icon for New Haven and see what exit zones are active. Often, a port has more than one exit. If none listed, it's blockaded.