The Toughest Thirteen

13 extremely challenging swims for the advanced solo marathon swimmer. If the Oceans Seven are the “Everests” of open water, the Toughest Thirteen are the K2s.

The Toughest Thirteen (an MSF project) aims to inspire marathon swimmers to seek lesser-known, less frequently swum waters offering unique and extraordinary challenges. In 2019, over 200 swimmers have completed the Triple Crown, and many of the Oceans Seven swims have multi-year waiting lists. In contrast, for any of the T13 swims you may not have to wait longer than the next available good weather; and if you’re successful, you’ll be one of only a small handful.

Many of these swims have been DNF’d more often than finished!

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T13 Criteria

  • Repeatable route defined by natural geographical features.
  • Not unprecedented, but less frequently swum than any of the O7.
  • Significant history of failed swim attempts.
  • Geographical diversity: North America (4), British Isles (3), Australia & New Zealand (2), Europe (1), Pacific (1), Latin America (1), Africa (1).
  • Route-type diversity: channel crossing (7), bay crossing (2), lake crossing (2), island loop (1), river (1).
  • Distance diversity: from 16 to 48 kilometers (10 to 30 miles).

ʻAlenuihāhā Channel

A minimum 48 km channel swim between the islands of Hawaii and Maui. Challenges include strong winds, large swells, variable currents, and wildlife. Monitored by the Hawaii Channel Swimming Association.

Four successful swims since 1970:

ʻAlenuihāhā Channel (source)

Maui to/from Hawaii (Big Island)


A minimum 19 km channel swim across the Fehmarn Belt in the Baltic Sea, between the islands of Fehmarn, Germany, and Lolland, Denmark. Challenges include cold water, unstable weather, and cross-currents. Monitored by Beltquerung.

Thirty-six successful swims since 1939.

Beltquerung (source)

Fehmarn (Germany) to/from Lolland (Denmark)

Dál Riata Channel

A minimum 21 km channel swim between Scotland and Northern Ireland. An alternate, more northerly route of the North Channel, shorter but arguably more challenging due to colder water and stronger currents. Monitored by the Irish Long Distance Swimming Association.

First attempted by Mercedes Gleitze in 1928. Two successful swims since 2012:

Dál Riata Channel (source)

Mull of Kintyre (Scotland) to/from Torr Head (Northern Ireland)

Derwent River

A 34 km swim in the Derwent River, Tasmania from the New Norfolk Bridge to the Tasman Bridge. Challenges include cold water and unstable weather. Monitored by Chris Guesdon.

First attempted by Chris Guesdon in 1973 as the “Derwent River Big Swim.” Six successful swims since 1975.

Derwent River (source)

New Norfolk Bridge to Tasman Bridge

False Bay

A 33-37 km crossing of the width of False Bay, South Africa, between Cape Point and Cape Hangklip. Challenges include unstable weather and white sharks. Sanctioned by the False Bay Swimming Association

Five successful swims since 1989:

False Bay (source)

Pringle Bay to Buffels Bay

Fastnet Rock

An 16-21 km channel swim between Fastnet Rock and mainland Ireland (county Cork). Alternate routes include a 42 km loop around Fastnet, starting and finishing on the mainland. Challenges include cold water, unstable weather, and jellies. Monitored by Fastnet Swim.

10 successful swims since 2011.

Fastnet Rock (source)

Fastnet Rock to/from Baltimore or Schull

Foveaux Strait

A minimum 29 km channel swim between the South Island and Stewart Island (Rakiura) in New Zealand. Challenges include cold water, unstable weather, and strong cross-currents.

Eight successful swims since 1963:

Foveaux Strait (source)

Stewart Island to/from Bluff, South Island

Gulf of the Farallones

A channel swim between the Farallon Islands and the California mainland. Of the five successful solo swims since 1967, two finished on the Marin County coast (33-41 km), and three finished at the Golden Gate Bridge (48 km). Challenges include cold water, strong tides, unstable weather, and white sharks.

Gulf of the Farallones (source)

Farallon Islands to/from Golden Gate Bridge or Marin Headlands

Loch Ness

A 36 km lengthwise crossing of Loch Ness, Scotland, between Fort Augustus and Loch End. Challenges include cold water and unstable weather. Monitored by the British Long Distance Swimming Association.

Twenty-four successful swims since 1966, including a two-way crossing by David Morgan.

Loch Ness (source)

Fort Augustus to/from Loch End

Monterey Bay

A 37-40 km crossing of the width of Monterey Bay, between its two major cities, Santa Cruz and Monterey. Challenges include cold water, wind, waves, and wildlife (stinging and toothy). Sanctioned by the Monterey Bay Swimming Association.

Five successful swims since 1980:

Monterey Bay (source)

Monterey to/from Santa Cruz

Round-Trip Angel Island

A minimum 16 km loop around Angel Island from Aquatic Park, in San Francisco Bay. Challeges include strong cross-currents, cold water, wind, and heavy marine traffic.

27 successful swims since 1984:

Round-Trip Angel Island (source)

Loop around Angel Island from Aquatic Park

Strait of Juan de Fuca

A 16-30 km channel swim between Washington state (USA) and British Columbia (Canada). Challenges include cold water, strong cross-currents, and unstable weather. Sanctioned by the Northwest Open Water Swimming Association.

Eight successful swims since 1955:

Strait of Juan de Fuca (source)

Washington (USA) to/from British Columbia (Canada)

Lago Titicaca

A minimum 15 km route in Lago Titicaca (Bolivia and Peru). Challenges include high altitude (3812m / 12,500 ft) and cold water.

Note: A canonical marathon swim route in Lago Titicaca has not yet been established. The only known Titicaca marathon swim was completed by Lynne Cox in 1991 - a coastal 15km route between Copacabana, Bolivia and Chimbo, Peru. To qualify for the T13, swimmers must complete a route of at least 15km. If a longer, cross-lake route is pioneered in the future, we may revise/raise the minimum standard for a T13-qualifying Titicaca swim.

Lago Titicaca (source)

Minimum 15km route