Just off Highway 137, a mile north of where the 2018 lava flow swallowed the Kapoho Tidepools, three jet-black basins fill and drain with the Pacific swell. Locals call them Mermaid Ponds, and they are among the last swimming spots left in the Puna District after the eruption reshaped the coastline. This article covers where to find these pools, how to time the tides safely, and what else to know before you go.
Three main bodies of water, depths overhead, bordered by hala trees and a seawall that disappears at high tide.
The 2018 Lower Puna Eruption filled in Pohoiki Bay with sand and nearly destroyed Isaac Hale Beach Park. Mermaid Ponds survived because they sit on a stretch of lava that the flow bypassed. They are not a single pool but a straight-line complex of three main basins plus a shallow side pool, each with different exposure to the open ocean.
Mermaid Ponds are worth the drive, but safe swimming depends entirely on reading the ocean. Low tide can leave basins nearly dry, and rogue waves at high tide turn the pools into whirlpools. The middle pool, set back from the seawall, is the calmest option — especially for inexperienced swimmers.
Navigating the Puna Coast and Kona’s Black Lava Shoreline
The Big Island’s black lava shoreline is not one continuous feature. The Puna District, where Mermaid Ponds sit, is a young volcanic coast shaped by Kīlauea’s eruptions. To the west, the Kona Coast offers a different kind of access: Kiholo Bay requires a 15- to 20-minute hike across hardened lava fields from a highway pulloff. Both locations share dark volcanic rock and clear water, but the experience of getting there differs sharply. Puna’s ponds are roadside; Kiholo Bay demands a walk under direct sun.
One honest limitation: Mermaid Ponds has no facilities. No restrooms, no lifeguards, no shade beyond the hala trees. The Kona side has more infrastructure, but the tradeoff is the hike. Neither location suits someone looking for a resort-style beach day.
The Main Tide Pools and Where to Swim
Mermaid Ponds: Reading the Basins
Three main bodies of water run parallel to the coast. The first and last pools take the brunt of incoming swell. When waves surge, the protective seawall — a natural lava barrier — disappears underwater, and rogue waves can slam swimmers against the rocks or suck them back out to sea. The middle pool sits farther back from the seawall and stays calm even when the others churn. A scattering of flat-topped rocks at its edge works for sunbathing, though the surface is littered with shell fragments and bits of coral.
Inside the pools, schools of colorful fish trapped by the ebbing tide share the water with tiny black crabs, sea stars, urchins, and Hawaiian limpets called opihi. Hawaiian green sea turtles cruise the waves just beyond the seawall. On clear afternoons, the silhouette of Mauna Kea appears far inland — a reminder that the same volcanic forces that built the mountain also formed these basins.
The ideal time to swim is a few hours after high tide on a sunny, calm day with little wind. Very low tide drains the pools nearly dry several times a month. Check a tide chart before driving out from Pahoa.
Kiholo Bay: A Lava Tube Swimming Hole
On the Kona Coast, Kiholo Bay offers a different kind of black lava swimming experience. A lava tube formed by ancient volcanic activity created a natural pool with protected waters. Visibility often exceeds 100 feet. Morning visits provide the best chance to see Hawaiian green sea turtles basking on warm lava rocks or gliding through shallow water. The site stays uncrowded because of the short hike across exposed lava, which can be punishing in midday heat.
Practical Planning: Tides, Access, and Timing
Timing at Mermaid Ponds is not optional. The difference between a calm swim and a dangerous surge is a matter of hours.
| Condition | What Happens | Best For |
|---|---|---|
| Low tide | Water levels drop; pools may drain completely | Exploring rock pools, not swimming |
| High tide (calm day) | Pools fill; seawall partially submerged | Swimming in the middle pool only |
| High tide (high surf) | Rogue waves; whirlpool effect | Avoid entirely |
| Few hours after high tide | Stable water levels, minimal wave action | Ideal swimming window |
Getting There
From the town of Pahoa, follow Highway 132 past Lava Tree State Park. Less than half a mile beyond the park turnoff, the roadside turns into jet-black lavafield — the aftermath of the 2018 eruption, which destroyed several miles of Highway 132 before it was rebuilt. At the bottom of the hill, the defunct Kumukahi Lighthouse is visible. Turn left onto Government Beach Road (Highway 137) and continue for roughly four miles. Look for an abrupt S-curve with a painted yellow gate and low mortared lava rock wall on the right. Park off the pavement and walk along the edge of the wall to bypass it.
At high tide, much of the protective seawall disappears underwater. Rogue waves can explode over the banks and temporarily turn the ponds into whirlpools, slamming swimmers against the rocks. Safely experiencing Mermaid Ponds is completely dependent on ocean conditions.
Best Time of Year and Day
Sunny afternoons with little wind are the safest bet. The jet-black lava absorbs heat, and on clear East Hawaii afternoons the pools warm into bath-like temperatures. Morning visits at Kiholo Bay offer better turtle sightings and cooler hiking conditions across the lava fields. Winter brings larger surf to the Puna coast, narrowing the safe windows considerably.
On the Ground: What to Know Before You Go
Footwear and the Rocky Bottom
The pools have rocky bottoms littered with shell fragments and bits of coral. Water shoes or reef booties prevent cuts. The surrounding lava rock is sharp and uneven — barefoot navigation between basins is not practical.
What to Bring
No vendors operate at either location. Bring fresh water, sun protection, and snacks. A towel and a change of clothes are useful — the ponds leave a salty film, and the drive back to Pahoa involves unpaved sections. A waterproof pouch for phones and keys helps, especially if you plan to swim in the middle pool where the water depth reaches overhead.
For underwater visibility, a compact action camera like the DJI Osmo Action 6 Bundle handles the mix of bright surface light and darker lava-bottom shadows well, and its 8K resolution captures the detail of trapped fish and coral fragments without needing a separate housing.
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Local Etiquette and Rules
Taking sand or rocks from Punaluʻu Black Sand Beach is banned, and the same respect applies at Mermaid Ponds. The basalt sand along the Big Island’s shores breaks down much faster than quartz sand on continental beaches — it is young and fragile, and the beach needs fresh volcanic material from Kīlauea or Mauna Loa to survive. Removing material accelerates erosion. Leave the cowrie shells and angel clams where you find them.
Visitor Questions About the Big Island’s Black Lava Pools
Are Mermaid Ponds safe for children?
The middle pool is set back from the seawall and stays calm when the outer pools churn, making it the safest option for inexperienced swimmers. But the rocky bottom, overhead depths, and risk of rogue waves mean constant supervision is necessary. High tide days with surf should be avoided entirely.
How do the tidal pools compare to Punaluʻu Black Sand Beach?
Punaluʻu offers a broad black sand beach with freshwater springs bubbling up from the seafloor — you can feel a chilly thermocline where cool fresh water floats on warmer ocean water. Mermaid Ponds are enclosed lava basins with no sand and no spring-fed layer. Punaluʻu is better for a traditional beach visit; the ponds suit swimmers who want protected, fish-filled water.
Do I need a guide to find the lava tube swimming hole at Kiholo Bay?
No guide is required, but the hike across exposed lava fields can be disorienting under midday sun. The trail is unmarked in sections, and the lava tube entrance is not obvious. Morning visits reduce heat exposure and improve your chances of spotting Hawaiian green sea turtles basking on the rocks near the pool.
What happened to the old Kapoho Tidepools?
The 2018 Lower Puna Eruption engulfed the Kapoho Tidepools and Ahalanui Beach Park completely. Mermaid Ponds, located a mile or two north of the lava field’s edge, survived because the flow stopped short. They now serve as one of the few remaining swimming spots in the Puna District.
Is the water in Mermaid Ponds warm?
On clear afternoons, the jet-black lava absorbs enough heat to turn the pools into warm, salty bathtubs. The temperature varies with tide and cloud cover — cooler water flushes in at high tide, and the pools warm again as the sun hits the exposed rock.
Closing
Mermaid Ponds and Kiholo Bay both sit on the same volcanic foundation, but they reward different kinds of effort. One is a roadside find that demands tidal literacy; the other trades convenience for solitude and a lava tube you can swim through. A Big Island road trip that connects the Puna pools with the Kona coast gives you two distinct versions of the same black lava shoreline — and a reason to check the tide chart before leaving the hotel.
Sources and further reading
Mermaid Ponds: Isolated, tranquil lava rock tidal pools great for swimming and sunbathing. Big Island.org.
Kiholo Bay: Secluded black lava beach with a secret lava tube swimming hole. Big Island Activities.
Punaluʻu Black Sand Beach geological formation. Things to Do Hawaii.
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