Open Water Progressive Build: 2500m Endurance Swim

Session Overview

This 60-minute open water session uses a progressive build structure to develop both endurance and pace awareness in non-pool conditions. Starting easy and building to race effort, 2500m covers the distance between Olympic (1500m) and 70.3 (1900m) race distances — making it excellent preparation for either. Complete this session regularly throughout the open water season.

What You’ll Need

• Wetsuit (if water temperature below 22°C)
• Safety buoy (always carry in open water)
• GPS watch with open water swim mode
• Swim goggles and silicone cap
• Swimming partner or lifeguard supervision

Warm-Up (10 Minutes)

Ease into the open water environment. Cold shock can spike heart rate — take your time before pressing on.

• 500m very easy — Zone 1, let your body adapt to the water temperature
• Focus on getting your breathing under control and finding your rhythm
• Practise sighting every 10–12 strokes during the warm-up

Main Set

Build through four distinct effort levels. Each 500m block should feel noticeably harder than the last — use your GPS pace or perceived effort to track the build. By the final block you should be working at genuine race intensity.

• 500m at Zone 2 (easy, comfortable, conversation-pace effort): find your rhythm
• 500m at Zone 3 (moderate, slightly uncomfortable): start working harder
• 500m at Zone 4 (threshold — your CSS or faster): proper effort required
• 500m at race effort (as if this were the final kilometre of your race): give it everything
• No rest between blocks — continuous swim throughout

Cool-Down (10 Minutes)

Drop back to easy effort and allow your heart rate to lower before exiting the water.

• 500m easy — very relaxed, focus on long strokes and proper recovery

Coaching Notes

• Never swim open water alone — always tell someone where you are swimming
• Sight every 8–10 strokes to stay on course and avoid adding distance
• If wetsuit buoyancy allows, use this session to practise swimming without a pull buoy — it transfers differently
• Note your GPS pace at each zone — compare pool pace to open water pace to understand your deficit
• Make it easier: reduce to 2000m total or shorten the race-effort block to 250m