Dorney Lake Triathlon
Eton Dorney, United Kingdom · August · Independent (RunThrough / Human Race / others at Eton Dorney)
Course: 1.5 km (0.9 mi) swim, 38 km (23.6 mi) bike, 10 km (6.2 mi) run. 2024 pack: 38 km (23.6 mi) bike; other years 40 km (24.9 mi). 0.93 mi swim, 6.2 mi run.
Why people love it
- Calm, clear Olympic rowing lake with a simple 750 m (820 yd) rectangular swim.
- Dead flat, traffic-free tarmac with about 3 m (10 ft) of gain per lap.
- Sprint and first-timer formats suit a first race, including shorter super sprints.
- One transition and free on-site parking make for a simple day trip.
- Heathrow is about 12 km (7.5 mi) away.
Watch out for
- Open lake is exposed: expect a headwind on one side of each 5 km (3.1 mi) loop.
- Parking can be up to a 20-minute walk (about 1 km (0.6 mi) / 0.6 mi) to registration.
- No shade on the run; late waves run in midday heat.
- Distances vary by organiser and date: Standard bike is 38 or 40 km (23.6 or 24.9 mi).
- Changing rooms are not always provided, so arrive ready to race.
Race
How racers feel about it, how well it is run, and how it treats a first timer. Counts for 30% of the overall score.
Toughness: Moderate
- Racer satisfactionLoved3.9
Racers in 2014, 2017 and 2022 praised the clear water and flat course. Wind and a long food queue were the gripes. · Low confidence
- OrganizationWell run4.0
Smooth waves and efficient marshals in 2014 and 2017. A crowded start pen and slow post-race food queue were noted. · Medium confidence
- First timer friendlyFriendly3.9
Calm lake and flat loops, but two swim laps and a long, exposed bike are a step up from the sprint. · Medium confidence
Course traits, not part of the score
- PR potentialFast4.1
Flat, closed and calm; the Standard bike is 38 or 40 km (23.6 or 24.9 mi) depending on the date. · Medium confidence
Swim
Wetsuit odds, water temperature, calm, and the experience of the start. Counts for 16% of the overall score.
- Wetsuit legalUsually4.2
UK lake likely 17 to 21 °C (63 to 70 °F), well under the 24.6 °C (76.3 °F) limit. A hot spell could ban suits. · Low confidence
- Water temperatureComfortable3.6
Estimated 17 to 21 °C (63 to 70 °F), cool early and late in the season. Comfortable in a wetsuit. · Low confidence
- Calm waterGlassy4.6
Sheltered purpose-built rowing lake. Racers report calm, clear water, though wind can ripple the surface. · Medium confidence
- Swim easeEasy4.3
1.5 km (0.93 mi) as two laps of a simple rectangle in calm water. · Medium confidence
- Swim experienceGreat3.9
Clean, clear water that one reviewer loved. Start pen can be crowded and the setting is functional, not scenic. · Medium confidence
- Swim supportGood4.0
Wave starts, a buoyed rectangle, rope lane markers and a thorough briefing. The start pen can be crowded. · Medium confidence
Bike
Road surface, closures, scenery and wind. Counts for 18% of the overall score.
- Road surfaceGood4.3
Smooth tarmac service road, wide enough for passing. One chicane to watch. · Medium confidence
- Road closuresFully closed4.8
Private, traffic-free venue road with no open traffic. · High confidence
- Bike sceneryPleasant2.9
Flat lakeside loops: pleasant in sun, but repetitive. · Medium confidence
- WindWindy2.3
Several racers call the lake extremely exposed, with a headwind on one side of each loop. · Medium confidence
Course traits, not part of the score
- Bike speedFast4.1
Fast and flat, though a headwind half of each lap and a chicane slow it. · Medium confidence
- Bike flatnessPancake flat4.8
Dead flat 5 km (3.1 mi) laps, about 3 m (10 ft) of gain each. · High confidence
- Bike simplicityMostly simple4.0
Simple loops, though a left-right-left chicane after transition and being lapped by faster riders need care. · Medium confidence
Run
Crowds, aid stations, conditions underfoot and scenery. Counts for 13% of the overall score.
- Crowd supportDecent3.3
Spectators gather near transition and see riders about eight times. Quiet elsewhere. · Low confidence
- Aid stationsGood3.6
Drinks at the far and near turns of each run lap. No shortages reported. · Low confidence
- Run sceneryPleasant2.9
Out-and-back lakeside path with open views. · Low confidence
- Run conditionsEasy3.5
10 km (6.2 mi) with no shade; later waves face midday heat. · Low confidence
Course traits, not part of the score
- Run flatnessFlat4.8
Flat lakeside path over 10 km (6.2 mi). · Medium confidence
Conditions
Air temperature, how predictable the weather is, setting, and spectating. Counts for 13% of the overall score.
- Air temperaturePleasant3.9
UK summer highs are roughly 18 to 24 °C (64 to 75 °F). Estimated, and hot spells are possible. · Low confidence
- Weather reliabilityVariable3.1
Mostly dry UK summer, but one report was nearly windless and others describe strong wind. · Medium confidence
- Venue beautyPleasant3.3
Olympic rowing lake with trees and open views. Clean but functional. · Medium confidence
- Spectator friendlyEasy4.3
Compact venue where family can watch the swim, transition and loops from one place. · Medium confidence
Course traits, not part of the score
- Low altitudeSea level5.0
About 25 m (82 ft) above sea level. · High confidence
Stay and travel
Hotels, walkability, getting there, and the town around the race. Counts for 10% of the overall score.
- Hotel availabilityGood3.8
Windsor, Slough and Heathrow hotels are close. No sell-out problems found. · Low confidence
- Hotel valueNormal3.2
Windsor is pricey; rooms toward Slough and Heathrow are cheaper. · Low confidence
- WalkabilitySome driving3.2
Free parking is up to a 20-minute walk (about 1 km (0.6 mi) / 0.6 mi) from registration. Swim, transition and run are together. · Medium confidence
- Travel easeVery easy4.5
About 12 km (7.5 mi) from Heathrow and close to the M4 and M25. · High confidence
- LogisticsSimple4.2
One transition at the lake, race-day registration and free parking. Changing facilities vary by date. · Medium confidence
- Town and foodFine3.4
Eton and Windsor have good cafes and pubs a short drive away. Nothing on site beyond race food. · Low confidence
Key facts
- Location
- Eton Dorney, Buckinghamshire, United Kingdom
- Typical month
- August
- Latest or next date
- 3 October 2026
- Organiser
- Independent (RunThrough / Human Race / others at Eton Dorney)
- Field size
- About 1,500 athletes
- Distances (non-standard)
- 1.5 km (0.9 mi) swim, 38 km (23.6 mi) bike, 10 km (6.2 mi) run
- Swim venue
- Eton College Rowing Centre (Dorney Lake), 2012 Olympic rowing lake (lake)
- Water temperature
- 17–21 °C (63–70 °F)
- Wetsuit
- Optional
- Swim start
- wave
- Swim laps
- 2
- Bike climbing
- 3 m (10 ft)
- Bike laps
- 8
- Key climbs
- Small bridge on return side, about 3 m (10 ft)
- Run climbing
- 0 m (0 ft)
- Run shade
- None (open lake)
- Air temperature
- 14–24 °C (57–75 °F)
- Humidity
- Moderate
- Altitude
- 25 m (82 ft)
- Nearest airport
- London Heathrow (LHR), 12 km (7 mi) away
- Where to stay
- Windsor, Eton
- Booking
- Windsor, Slough and Eton hotels nearby; no race-week squeeze found.
What racers and reviewers say
- RacecheckRaced 2017 · aggregator · Positive
Rated 4.4 out of 5 and recommended. Loved the clear water and strict but efficient marshalling; quick registration; plentiful parking but about a 20-minute walk to the race centre. Bike fast and flat and humbling if lapped; run had no shade in midday heat and the post-race food queue was long.
“well organised”
- Steel City StridersRaced 2022 · blog · Positive
A first-time triathlete's club write-up of the season finale: first-class venue with calm water and a flat, fast bike and run. A first-timers option (200 m (656 ft) / 220 yd swim, 5.3 km (3.3 mi) / 3.3 mi bike, 2.5 km (1.6 mi) / 1.6 mi run) ran alongside the Olympic.
- RunThrough race information (2024)Raced 2024 · article · Positive
Organiser race pack: clockwise rectangular 750 m (820 yd) swim, anticlockwise 5 km (3.1 mi) bike laps, drinks at the far and near run turns, and a hard-standing car park near the boathouse with overflow up to a 20-minute walk away.
- Addiscombe forumforum · Mixed
Club thread (snippet only, page had errors): a duathlon report calls the lake extremely exposed with head wind then tail wind on out-and-back loops; a women-only event report found the bike pretty awful in the wind.
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Sources
Pages we used for facts and ratings. See how we rate.
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