3km Open Water Endurance Swim: Long-Course Swim Training Session

Session Overview

This 3km continuous open water endurance swim builds the aerobic base and mental resilience required for 70.3 and IRONMAN swim legs. Designed for advanced swimmers comfortable in open water, it focuses on sustained effort, efficient sighting and maintaining stroke quality over distance.

What You Will Need

• Wetsuit (recommended for UK waters below 20 degrees Celsius)
• Tow float (mandatory for solo open water swimming)
• Swim cap and goggles
• GPS watch with open water swim mode (optional but useful for tracking distance)

Warm-Up (10 minutes)

Enter the water slowly and allow 3-5 minutes for cold water adaptation before starting your session timer. Swim two easy laps of a short loop at RPE 4/10, focusing on long, relaxed strokes and regular sighting practice. Use this time to check your goggles seal correctly and identify your sighting landmarks before the main set begins.

Main Set

Complete 3km continuously at a steady aerobic pace (RPE 6-7/10). You should be working hard enough that you would not want to hold a conversation, but not so hard that your stroke begins to break down. Divide the effort into three 1km segments in your mind:

• 0-1km: Settle into rhythm. Focus on relaxed, efficient strokes. Sight every 8-10 strokes.
• 1-2km: Maintain the same effort. Check your form: are your hips rotating? Is your catch early and high-elbow? Sight every 6-8 strokes.
• 2-3km: Build slightly if feeling strong, or hold your pace if fatiguing. Sight every 6 strokes as fatigue can cause drift in the final kilometre.

Cool-Down (10 minutes)

Swim 300-400m easy at RPE 3/10, focusing entirely on technique. Practice bilateral breathing if you normally breathe to one side. Exit the water slowly and get warm immediately — open water swim sessions in spring and autumn can result in a chill after exiting despite feeling warm in the water.

Coaching Notes

• Sighting frequency should increase when tired — fatigue causes drift even in calm conditions
• Common mistake: starting too fast in the first 500m and blowing up by 2km — treat this like a long run, not a race
• Scale down: complete 2km instead of 3km if you are newer to long open water swims; build to 3km over three to four sessions
• Scale up: add 3 x 200m build efforts at the end of the 3km for athletes targeting IRONMAN swim times under 1 hour