Can't recall the marshes flooding in the 20 years I've been living in Greater Boston. It's well-protected from storm surge by Nahant, eliminating the biggest risk. Springtime rains and snowmelt aren't really enough for causing problems from the inland side. The drainage is poor because of the decades of silt buildup, and the whole river could really use a dredging to improve the ecosystem in Rumney Marsh as the curtailed flow starves the river of oxygen. But it's a least concern for nearby structures because the brunt of it gets absorbed by the empty conservation land.
Salem, on the other hand, gets a North River inundation that turns the rail tunnel into a storm drain about once per decade. East-west from downtown Salem to downtown Peabody has notorious flooding problems affecting both rail lines and intersecting thoroughfares, severe risk of a really bad 50-year flooding event from an ocean storm causing big damage, and lots of previously accrued damage (e.g. lots of problems with sinkholes on local streets from washed-out substrate) that needs a major infrastructure renewal investment. Mouth of North River faces northeast into open ocean with nothing blocking it. And like Saugus River it is similarly silt-choked with poor drainage and is overdue for a dredging, making it handle rainwater drainage very poorly. Unlike Saugus River surrounded by the marsh, North River (and to lesser extent Danvers River) has urban density abutting it for its whole length. The densest parts of Salem and Peabody and all critical infrastructure therein end up unusually vulnerable for frequent minor inundations causing low-level damage through pressure and time, and risk of a 'Perfect Storm'-level event from precisely the wrong wind direction causing catastrophic damage when the silty inlets can't drain a storm surge nearly as well as they used to.
