We live a 5 minute drive from a marina, less than 2km by foot. I have often considered bug-out-by-water as one of our options, especially given how close we live to the Bay and that has been one of the motivators I've had to get into kayaking.
The marina we live near features a 280m long pier, which meats up with a 350m long, curved piled stone breakwater which protects a anchorage with around 120 berths, most of which are suited to docking 2 small yachts.
Both the pier and the breakwater are topped with concrete slab walkways and fitted with guard rails on the windward side. The pier has its own small floating dock and we often see fishermen trying their hand to catch the fish that inhabit the bay from it in the evenings.
The breakwater has a harbourmasters hut, on a raised platform around its 250m mark, and at this point, it is around 240m away from the closest point of the spit of sand that makes up the closest bit of shore.
The marina proper is walled, with heavy duty fencing wrapping around its pier-side perimeter, with spiked ramparts, the marina's facilities are well protected from casual intruders. A motivated individual could make it over these walls without too much trouble, or even less if you approach it from the water, but this is designed to keep people from wandering into private property and making off with supplies, or interfering with the docked vessels.
A variety of small boats are docked here, from yachts to a few powered launches and even a couple of small sport fishing boats, with a selection of runabouts mored to the marina walls as well. There are only limited facilities in the walled off marina section, but it is both raised from the water level, and walled off from the pier.
These traits are what make me consider the marina and the pier as bug-out locations. They are removed from the main thoroughfare of modern urban life, whilst being not too distant as to make it untenable to range out from.
The sparse local resources bring both a risk and a boon. Apart from the boats, there is little to salvage or scavenge, which would reduce its value as a raiding target to most people. If the threat faced required isolation, say a quarantine, and there were not many able-bodied people to worry about breaking that quarantine this might well make a very appealing site. Prevailing winds and the action of the waves give you some sound and smoke dissipation concealment, and by the very nature of location, you might well have the advantage of obscurity. Assuming you were not concerned with natural risks coming from the water, or weather, or from able-bodied threats able to invade from the sea, a location like a marina might well make a good bug-out location to head for, even if you don't intend to use it as a staging point to flee by boat, their primary resource.