Casco Bay Islands Flood Zones: What FEMA's Maps Do (and Don't) Tell You

How FEMA Flood Zones Work, in Plain Terms

FEMA flood zones are a nationally standardized system, and the same letter codes appear on Flood Insurance Rate Maps everywhere in the country, island or mainland. Zone X generally denotes minimal-to-moderate flood risk, outside the mapped 1-percent-annual-chance floodplain. Zone AE denotes areas within that 1-percent-annual-chance floodplain where a base flood elevation has been calculated -- the zone most commonly tied to the federally required flood insurance purchase on a mortgaged property. Zone VE denotes the highest-risk coastal category: land subject to the 1-percent-annual-chance flood plus additional hazard from storm-driven wave action, typically the shoreline areas closest to open water. These are general, well-documented FEMA definitions, not specific findings about Long Island, Chebeague, Great Diamond, Little Diamond, or Cliff Island.

This page will not attach any of those codes to a specific dock, road, or lot on any of these five islands. FEMA draws flood zone boundaries parcel by parcel, updates them periodically, and the only responsible way to know which zone applies to a given property is to look it up directly on FEMA's own map -- not to infer it from an island's general shape or from a page like this one.

Five Islands, Five Different Shapes -- What's Actually Confirmed About Land Area

These five islands are not a single landmass and are not uniformly at risk. Long Island's incorporated town has a total area of 33.52 square miles, but that figure is almost entirely water -- 32.10 square miles of it. The actual land area is just 1.42 square miles, with the main island commonly described as roughly three miles long and about a mile wide. A small land area relative to a large surrounding-water total is itself a rough proxy for how much of the town's footprint is shoreline rather than deep interior -- worth knowing generically, though it is not a substitute for an actual elevation or flood-zone reading.

Chebeague Island, the largest of these five communities, has a total area of 24.56 square miles (3.56 square miles land, 21.00 square miles water). Great Chebeague Island itself -- the main inhabited landmass -- is roughly 1,930 acres, described as nearly 5 miles long and about 1.5 miles wide, giving it meaningfully more interior high ground to work with than Long Island's much smaller land footprint.

For Great Diamond Island, Little Diamond Island, and Cliff Island, a specific confirmed land-area figure was not available in the research behind this page -- flagged here as a genuine gap rather than filled in with an estimate. Cliff Island's shape is commonly described as roughly "H-shaped," and it is known to be the farthest and longest ferry run of the five, but that is a description of shape and distance, not a substitute for acreage or elevation data.

The January 2024 Storms: Real Regional Damage, Not a Confirmed Island-by-Island Report

Two back-to-back storms in January 2024 caused serious, well-documented damage across Casco Bay. Eagle Island -- a state historic site -- lost three of four stone cribs supporting its pier and suffered significant erosion at its southern end, closing it for the 2024 season. Lanes Island, off Freeport, had a campsite threatened by beach erosion. Little Chebeague, Bangs, and Crow Islands were documented as damaged. Whaleboat Island, Little Whaleboat, and The Goslings in Middle Bay, along with Monroe and Sheep Islands, also saw documented storm effects, including trail systems blocked by storm-felled trees. A stewardship manager for the Maine Island Trail Association called the damage "beyond anything I've seen" in twelve years with the organization.

Here is the honest part: that reporting did not name Long Island, Chebeague Island, Great Diamond Island, Little Diamond Island, or Cliff Island specifically. Given how severe and widespread the documented damage was elsewhere in the bay that same weekend, it is a reasonable inference that these five islands likely saw some effects too -- but that is an inference, not a confirmed fact, and this page will not present it as one. If you are evaluating a specific property on any of these islands, ask the seller, a local contractor, or the town office directly whether that property saw any effects from the January 2024 storms, rather than relying on regional reporting that never named these islands by name.

Ferry Dependency Is Its Own Storm-Risk Factor

Something a mainland coastal town does not face: every one of these islands' emergency response, evacuation, and post-storm supply and repair logistics runs through Casco Bay Lines -- and, for Chebeague Island specifically, also through the Chebeague Transportation Company's separate route from Cousins Island in Yarmouth. A storm severe enough to disrupt ferry service can delay evacuation, emergency response, or simply getting a generator or plywood to the island, in a way that a bridge- or road-connected coastal community does not experience. No specific island-by-island evacuation plan or ferry-suspension protocol for a storm event was confirmed in the research behind this page, but the structural dependency itself is real and worth weighing alongside any flood-zone conversation.

Friends of Casco Bay maintains its own public resource on rising seas and storm surges in Casco Bay, and that resource addresses the broader bay as a whole, not any one of these five islands specifically. Treat it as useful regional background on sea-level trends in Casco Bay generally, not as an island-specific erosion rate or flood-zone finding for Long Island, Chebeague, Great Diamond, Little Diamond, or Cliff Island.

Where to Actually Verify a Flood Zone -- and Who to Call Depends on Which Island

Unlike Peaks Island, which is a City of Portland neighborhood with one governing city hall, this market splits into two different kinds of local government. Long Island and Chebeague Island are each their own incorporated town -- Long Island seceded from the City of Portland on July 1, 1993, and Chebeague Island seceded from the town of Cumberland, Maine, on July 1, 2007 -- which means each has its own town office to contact for local floodplain-management questions, permitting, and building-code provisions. Great Diamond Island, Little Diamond Island, and Cliff Island, by contrast, have never been separate towns; they are Portland neighborhoods, so the relevant local authority for those three islands is the City of Portland's own building and planning department, the same office that handles floodplain questions for every other Portland neighborhood, Peaks Island included.

Whichever island you're looking at, the two-step check is the same: look up the specific address on FEMA's Flood Map Service Center (msc.fema.gov) to see the current official flood zone designation, and separately contact the right local office -- the Town of Long Island or Town of Chebeague Island for those two islands, or the City of Portland's building and planning department for Great Diamond, Little Diamond, and Cliff Island -- to confirm local floodplain rules and any permitting requirements tied to that zone. Neither step is something this page, or any general overview page, can substitute for.

What to Actually Verify Before You Decide

Put together, honestly: FEMA's flood zone letters (X, AE, VE, and the rest) are a standardized national system, and how they apply to any specific property on Long Island, Chebeague Island, Great Diamond Island, Little Diamond Island, or Cliff Island depends on that property's actual mapped location -- not on general statements about an island's overall shape, land area, or ferry access. This page has deliberately avoided naming a flood zone for any part of any of these five islands because no specific zone assignment was confirmed in the research behind it, and it has deliberately declined to treat the January 2024 Casco Bay storm damage as confirmed for these islands specifically, because the sourced reporting behind that event named other Casco Bay islands, not these five.

Before making any purchase, financing, or insurance decision that depends on flood-zone status, look up the specific address on FEMA's Flood Map Service Center and contact the correct local office for that island -- the Town of Long Island or Town of Chebeague Island's own town office for those two, or the City of Portland's building and planning department for Great Diamond, Little Diamond, and Cliff Island. Nothing on this page is insurance, engineering, or legal advice.