Diamond Mountain Triathlon

SEP
20
2026
Swim, bike, and run at Lake Welch Beach in Harriman State Park. The event offers triathlon and duathlon options for adults and free races for juniors. All finishers get a medal, and the course features scenic lake and park views.
Sun 20 Sep 2026
Adult Duathlon (2mi/15mi/... Adult Triathlon (0.5mi/15... Junior Duathlon (2mi/15mi... Junior Triathlon (0.5mi/1...

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Events

The Diamond Mountain Triathlon includes four events with different distances:

  • Adult Triathlon: 0.5 mi swim, 15 mi bike, 2 mi run
  • Adult Duathlon: 2 mi run, 15 mi bike, 2 mi run
  • Junior Triathlon: 0.5 mi swim, 15 mi bike, 2 mi run (for ages 15-18)
  • Junior Duathlon: 2 mi run, 15 mi bike, 2 mi run (for ages 15-18)

Registration for the Junior Triathlon and Duathlon is free.

Location and Course

The event is held at Lake Welch Beach in Harriman State Park, Stony Point, New York. The triathlon features a swim in Lake Welch. The bike course is one rolling 15-mile lap around the park, and the run is along the lakeside. The duathlon uses the same bike course and the same 2-mile run course for both segments.

Event Details

All participants receive a finisher medal. Awards are given to the top three men and women in both the triathlon and duathlon. The overall adult triathlon winners receive a special triathlon suit. Adult triathlon participants get a free jersey, and duathlon participants get a running jersey.

The event offers free public parking, open restrooms, and water available at check-in. The course features police-controlled intersections, signage, volunteer support, and race photographers. Wetsuits are permitted for the swim. Visit the organization's website for the most recent information.

Adult Duathlon (2mi/15mi/2mi)
Adult Triathlon (0.5mi/15mi/2mi)
Junior Duathlon (2mi/15mi/2mi)
Junior Triathlon (0.5mi/15mi/2mi)
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