The Portland Phoenix

Island swimming hole: Cool off in a quarry in Stonington Harbor

Heather Steeves and PJ Koroski

Heather Steeves, left, and PJ Koroski take the plunge in the quarry at Green Island Preserve in Stonington Harbor. (Portland Phoenix/Shannon Bryan)

A decent swimming hole has two essential qualities: the water is clean and the hole is deep enough to submerge your whole person.

Ideally, the water is also refreshingly cool and leech-free; extra points are added for rope swings and swimming-hole-adjacent waterfalls. 

Having spent my childhood summers cooling off by sitting in a bucket full of hose water in the middle of our suburban driveway, I tend to think every swimming hole is pretty glorious. I don’t even mind mucky pond bottoms or fish nibbling at my toes.

Heather Steeves paddles across Stonington Harbor to Green Island. (Portland Phoenix/Shannon Bryan)

But I can also recognize a standout swimming hole when I see one. The quarry on Green Island in Stonington Harbor is a standout swimming hole. 

Green Island is a 47-acre island about a half-mile off the coast of Stonington. Getting there requires a boat – motorized or a kayak powered by your own enthusiastic self – making the Green Island swimming hole so much more than a ho-hum way to cool off on a hot summer day. It’s an adventure. 

On the southeast side of the island, there’s a small cove with space to land a kayak as well as an old granite wharf with a wooden ladder for boaters. From there, the Green Island Preserve sign leads the way to a loop trail, a small meadow, and a swimming hole in an old quarry. 

The preserve is managed by Maine Coast Heritage Trust (it’s one of several MCHT preserves in the archipelago between Stonington and Isle au Haut. Others include Sand Island, Gooseberry, Pell Island, and Saddleback Island). The quarry, now flooded with rain water and surrounded by trees, is a swimmer’s delight. How it came to be is the result of cooled magma, a whole lot of time, and human influence. 

The well-marked path to the Green Island quarry, in the preserve managed by the Maine Coast Heritage Trust. (Portland Phoenix/Shannon Bryan)

The granite on Green Island formed 365-405 million years ago below the earth’s surface, and over the millennia, it was revealed by erosion. It remained embedded there until the 1870s when quarrying operations began, and the rock was extracted with help from pneumatic drills, explosives, and hand winches. By then, the island was known as Green Island, named for Sullivan Green, who purchased the property around 1840. 

According to a history of the island on the MCHT website, the Green Island quarries – one on the east side and one on the west side – were abandoned by 1923. The island changed hands a few times over the following decades; in the meantime, nature reclaimed the place, as nature tends to do. Spruce trees grew in abundance, crowding around the edges of the quarries like curious onlookers. Greenery proliferated, easing the harshness of the agitated landscape, and returning the island to a welcoming respite. 

Van and Mary Clark acquired the island some time prior to 1990, when a cruising guide published some juicy island intel: the small quarry on the east side of the island was a cool spot to swim. What had been a quiet swimming hole for locals suddenly got more popular, and the Clarks grew concerned about liability issues and water quality. Having long wished to protect the island, Mary Clark donated it to MCHT in 1993. 

PJ Koroski, left, and Heather Steeves enjoy the sights and sounds of the Green Island Preserve quarry in Stonington Harbor. (Portland Phoenix/Shannon Bryan)

Now the Green Island Preserve is a welcoming space for folks who’d like to frog-kick their way through the quarry-turned-swimming-hole or jump into the water from the quarry’s edge. (As with any swimming hole, think before you leap. It’s sometimes hard to tell how deep the water is in any given spot. The quarry stones are old, and there’s who-knows-what metal or glass stuff lying about. My point: have fun, don’t hurt yourself.)

There’s another important point to consider: How do you get there? 

When Heather Steeves, PJ Koroski, and I decided to head to Green Island by kayak for a swimming hole adventure in 2020, we departed from the Colwell Boat Ramp in Stonington. Green is about half a mile from the boat ramp, although you’ll need to paddle around the island to the southeastern side to land your boat and access the trail to the quarry. That year, we were lucky to score parking at the nearby Isle au Haut Boat Services wharf. Those spots tend to fill early, though, so reserving in advance is highly recommended. Other area businesses also often offer parking for a fee. 

Once launched, we headed straight to Green, opting to paddle around the north side of the island until we reached the cove. Boaters can tie up on the old granite wharf, but we paddlers dragged our kayaks up near the Green Island Preserve sign, which marks the trail access to the quarry. After a short walk, we came upon the quarry. A couple of swimmers were floating in the water, others sitting near the edge to eat lunch and soak up the sun. 

We spent the next couple of hours doing the same, enjoying this not-so-secret swimming hole that simultaneously feels like a newly discovered sanctuary and a time machine back through geologic and human history. And it’s clear why Mary Clark and the MCHT chose to protect this place. 

There is no camping allowed on Green Island, but if you opt to make a weekend of it, there are several nearby islands where you can pitch a tent and stay the night. Both the trust and the Maine Island Trail Association are excellent resources for that information. 

Taking a dip in an island quarry you had to kayak to is also the kind of adventure that will keep you feeling cool all summer. 

Shannon Bryan is a writer and outdoor enthusiast who lives in South Portland. Find her at

Getting there

Use the boat launch at Colwell Boat Ramp, Colwell Lane, Stonington, behind Isle au Haut Boat Services. Reserve parking in advance at Isle au Haut Boat Services: 207-367-5193.

For more info about Green Island and other preserves managed by Maine Coast Heritage Trust:

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