The Annisquam is a fairly large tidal river, with its mouth at the northern side of the narrowest part of Cape Ann. Its southernmost reaches are connected with Gloucester's massive harbor by a small cut, called the Blynman Canal. The latter is both short and narrow, with a drawbridge over it at its (southern) entrance called "the cut bridge." Northbound (as we were today, coming from Marblehead) there are two more bridges to deal with: the MBTA drawbridge, and the 128-fixed bridge. If your rig is more than 65-feet tall (highly unlikely for a shoal draft boat) do not attempt the Annisquam at all, as you will not fit under the 128 Bridge. The river is shown in detail on chart 13281, and is subject (like many tidal rivers) to constant shifts in the channel. Some passages are dredged, but as the primary users of the river and canal are pleasure craft, money for maintaining dredged channels is scarce, and we have heard reports that recent hurricanes and noreasters have wreaked havoc on them.
The tidal current rips hard through the channel, especially at the Gloucester Harbor end. The canal and drawbridges should not be navigated under sail under any circumstances, and (as the Cruising Guide notes) your engine needs to have both balls and the ability to work in reverse. Traffic in the canal and river on the weekends can be downright frightening, but on a weekday (like today) you have only the current to deal with, which is probably plenty. Counter-intuitively, coming into the canal against the current (that is on falling tide, for a Northbound/Eastbound traveller; rising, for the opposite) is easier than going with the current. It is a slower going, but you have more control over your boat. Going with the current can be unpleasantly like surfing.
If the conditions are right (the tide is high and you have an up-to-date chart) there are several tributary branches of the Annisquam, on both sides, that are worth exploring and maybe even anchoring in. Frankly we are reluctant to give names because we want to keep them to ourselves. But if you don't have a good chart and the ability to read it, it isn't safe to visit these places anyway.
If you prefer a sure thing, Cape Marina has slips, and Annisquam Yacht Club and the Market Restaurant in Lobster Cove both have moorings. The latter's moorings are more sheltered and are further up inside the cove, but they are also $50. What?! We went for it anyway. This the view.