A short history of underwater cave exploration: dated milestones

Underwater cave exploration is young. Most of the passages divers know today were first entered after the 1950s, and much of what is known about them comes from the survey archives and expedition reports of the people who explored them. This article gathers dated milestones from those records. Lengths and depths are snapshots: they change as exploration continues, and different sources measure different things (distance from an entrance, distance between two entrances, or depth below the surface).

Florida's early explorers

Florida's springs were the first great proving ground. The state park history for Peacock Springs records the first known cave dive there in 1956 ^[2]. The NSS Cave Diving Section's history describes the 1960s as a golden age of survey and mapping, when John Harper became the first American diver to lead teams regularly beyond the daylight zone; with Joe Fuller he made the first 1,000-foot (about 300 m) penetration, at Hornsby Sink, and doubled that distance for a traverse record in December 1962 ^[1].

In the following decade, according to the same history, explored underwater passage in Florida grew to roughly 200,000 feet (about 61 km), much of it first seen by Sheck Exley and his partners. Exley made early accurate surveys at Madison Blue Spring in 1970, and by the end of the 1970s the Peacock Springs system, surveyed by section members to 20,293 feet (about 6.2 km), was the longest underwater cave known ^[1]. In the 1980s it was overtaken by Lucayan Caverns in The Bahamas, explored and surveyed by section members to more than 30,000 feet (about 9 km), and then by Florida's Cathedral/Falmouth system ^[1].

Sheck Exley

Exley is the best-known figure of this period. Accounts credit him with being the first to log more than 1,000 cave dives and with more than 4,000 over about 29 years ^[3]. His 1979 booklet Basic Cave Diving: A Blueprint for Survival set out safety rules drawn from accident analysis ^[1], and the NSS Cave Diving Section now distributes it free of charge ^[21]. A biographical essay records a world-record depth of 881 feet (about 268 m) at the Nacimiento del Río Mante in Mexico in March 1989 and a penetration of more than two underwater miles (over 3 km) at Cathedral Canyon, Florida, in 1990 ^[3]. In August 1993 he reached the bottom of Boesmansgat in South Africa at 263 m ^[17]. Exley died on 1994-04-06 during a deep dive at Zacatón in Mexico, a sinkhole he was exploring with Jim Bowden ^[3].

Wakulla Springs, 1987 and 1998

Wakulla Spring, south of Tallahassee, was private for decades. The U.S. Deep Caving Team (USDCT) records that the State of Florida bought it in autumn 1986 from the estate of financier Edward Ball, and that before 1987 only two groups had been legally allowed inside: a late-1950s team led by Wally Jenkins and Gary Salsman that reached about 200 m, and a 1981 team of Paul DeLoach, Mary Ellen Eckhoff and John Zumrick that reached about 400 m ^[4].

The Wakulla Springs Project, led by Bill Stone, set out on 1987-10-24 with 20 people for a 70-day expedition ^[4]. Because the main tunnels lie more than 90 m deep, the team built a portable underwater habitat, a 3 m hemispherical shelter in which returning divers could wait out part of their decompression. Exley and DeLoach explored the main A-Tunnel, about 40 m wide, to 860 m in two dives; on 1987-12-04 Wes Skiles, Tom Morris and Paul Heinerth pushed B-Tunnel to 1,273 m, the longest penetration of the project. In all, seven tunnels totalling about 3,300 m were explored and surveyed. The project also tested the Cis-Lunar MK1 rebreather, including a 24-hour underwater run by Stone on 3-4 December ^[4].

The 1998 Wakulla 2 expedition aimed at mapping rather than distance. Its Digital Wall Mapper, mounted on a diver propulsion vehicle, used sonar and inertial navigation to record the shape of the passage walls in three dimensions ^[5][6]. A geology summary from the project reports that the resulting 1998-1999 map showed much of the cave floor sitting at about 90 m ^[20].

The Woodville Karst Plain Project

The Woodville Karst Plain Project (WKPP) traces its origins to the 1985 exploration of upstream Sullivan Sink. After many dives the team connected Sullivan to the Emerald system, which at 41,000 feet (about 12.5 km) was then, by the project's account, the longest underwater cave known. In May 1988 surveyor Bill McFaden died during a mapping dive, and the team began drafting deep-diving standards. On 1988-06-19 four divers traversed from Sullivan to Cheryl Sink, and on 1990-10-24 the National Speleological Society accepted the WKPP as an official project ^[7].

A 2007 WKPP fact sheet lists records that include a 13,000-foot (about 4 km) traverse from Big Dismal Sink to Cheryl Sink in 1999 and successive penetration records at Wakulla, the last of 23,810 feet (about 7.3 km) on 2007-06-23 ^[9]. On 2007-12-15 Jarrod Jablonski and Casey McKinlay swam from Turner Sink to Wakulla Springs, nearly seven miles (about 11 km), spending about seven hours at around 300 feet (about 90 m) followed by roughly 15 hours of decompression. The dive proved that the Leon Sinks and Wakulla systems were one, now known as the Wakulla-Leon Sinks Cave System ^[8].

Quintana Roo and the long caves

Exploration of the Quintana Roo aquifer began in the mid-1980s, according to the exploration group CINDAQ ^[19]. The NSS Cave Diving Section credits member Jim Coke and others with the first surveys of Dos Ojos, Xel-Ha, Naharon and Mayan Blue ^[1]. The Quintana Roo Speleological Survey (QRSS), created in 1990 to archive survey data, held by January 2025 confirmed data for 1,736.7 km of underwater passage in more than 412 caves ^[10].

The QRSS list for January 2025 ranks Sistema Ox Bel Ha first at 496,804 m (a CINDAQ figure dated October 2024) and Sistema Sac Actun second at 379,569 m with a depth of 119.2 m (December 2024) ^[11]. CINDAQ's 2025 report says a resurvey of Ox Bel Ha begun seven years earlier had re-measured almost all of the original 245 km, found more than 185 km of new passage, and brought the system to nearly 529 km ^[12]. The difference between the two figures reflects different dates and reporting, which is normal for systems still being explored. In 2007 one Sac Actun exploration team found Hoyo Negro, the pit that held the skeleton known as Naia ^[13].

Depth: Boesmansgat, Pozzo del Merro, Hranice and Pearse

Depth exploration followed a separate path. At Boesmansgat in South Africa, after Exley's 263 m in 1993, Nuno Gomes reached an averaged 282.6 m in August 1996, according to an account by Martyn Farr reproduced on Gomes's website ^[17].

At Pozzo del Merro near Rome, divers reached 100 m in 1998-1999, and in March 2002 a remotely operated vehicle (ROV) from the Italian fire service's dive unit reached 392 m without clearly finding the bottom ^[16].

The Hranice Abyss in the Czech Republic overtook it. Its local caving group records that Polish diver Krzysztof Starnawski passed a restriction in June 2012 and descended to 217 m, then set successive depth records, reaching 265 m on 2015-08-21. An ROV reached 404 m on 2016-09-27 ^[14], and in a July-August 2022 campaign an underwater robot reached 450 m before its technical limits stopped it; the bottom has still not been seen ^[15].

In New Zealand, a 2020 first-person article written by Richard Harris for the website of scooter maker Seacraft describes the Pearse Resurgence: he first dived it in 2007, when Dave Apperley and Rick Stanton extended it from 125 m to 177 m, and with the Wet Mules team it was later pushed to 229 m in one tunnel and 245 m in another, in water of about 6 °C ^[18].

Reading the record

Several cautions apply. Many of these figures come from the explorers' own accounts, which are valuable but not independent. Records of distance, traverse and depth are different achievements, and some recent depth figures belong to robots rather than divers. Behind the numbers are serious hazards: several pioneers named here died in caves. This article describes what happened and when; it is not a description of how such dives are done. The surveying article explains how the maps behind these figures are made.