Hot Weather Open Water Swim: Zone 2 to Zone 3 Build Session

Session Overview

This 45-minute open water session is designed for summer training in warmer conditions, helping you acclimatise to higher air and water temperatures while building race-specific aerobic fitness. You’ll progress gradually from an easy Zone 2 effort to a sustained Zone 3 tempo, learning how heat affects your pace and heart rate in a controlled way.

What You’ll Need

• Open water venue (lake, reservoir, or safe coastal spot)
• Wetsuit or swimskin depending on water temperature
• Safety tow buoy — mandatory for solo open water swims
• GPS watch (optional but useful for pacing)
• Water bottle for post-swim hydration

Warm-Up (10 minutes)

Enter the water gradually and spend the first 5 minutes at a very easy pace — barely above floating. Focus on sighting every 6-8 strokes to orient yourself and settle any initial anxiety. Use the remaining 5 minutes to build gently to your comfortable Zone 2 cruise pace, practising bilateral breathing and relaxed arm entry.

Main Set

The main set is a progressive build across four blocks. Choose a safe loop of approximately 200-400m and repeat it as needed to hit the distances. In hot weather, your Zone 2 pace will feel harder than in cooler conditions — that’s normal. Trust perceived effort, not pace.

• 10 minutes continuous easy (Zone 2) — breathe every 3 strokes, stay relaxed and controlled
• 60-second easy float or tread water — check your heart rate and notice heat awareness
• 8 minutes at comfortable pace (Zone 2 to low Zone 3) — slightly more purposeful strokes
• 60-second easy float or tread water
• 6 minutes at moderate effort (Zone 3) — pushing to race-comfortable effort
• 60 seconds easy
• 5 minutes at steady Zone 3 — hold this throughout without additional rest

Cool-Down (5 minutes)

Swim back to your exit point at a very easy, relaxed pace — long strokes, slow breathing. On exit, find shade immediately and begin rehydrating. Your core temperature will stay elevated for 10-15 minutes after a warm open water swim, so don’t rush changing or moving on.

Coaching Notes

• Heat increases your heart rate by 5-10bpm at the same effort — don’t panic if your monitor shows elevated readings. Use RPE alongside heart rate in warm conditions.
• Drink 500-750ml of water in the hour before this session. You lose fluid through sweating even while swimming in warm weather.
• Never swim alone in open water — always use a tow buoy and ideally have a support person on the bank or nearby.
• Make it easier: Stay at Zone 2 for the full main set and skip the Zone 3 push blocks.
• Make it harder: Extend the final Zone 3 block to 10 minutes and add a fourth progressive block at near-race effort.