The current heatwave on Zakynthos makes walking a little difficult at this time of year; however, several of the walks pass close to the sea, so, while you may not achieve the entire walk, sections of walks are ideal for finding swim spots far from the crowds, particularly if you are following one of the car tours around the island. For instance, the Gerakas to Daphni trail (walk 2 in Sunflower Books Complete guide to Zakynthos), runs along the shoreline, with reefs extending almost to Pelouso, which are rich in marine-life, including sea turtles.
The beach of Vrondonero (be warned it is unofficially nudist) on the Vrondonero walk (Walk 5) is also beautiful, with deep cool waters. Alternatively, the entire stretch of the Kalamaki Dunes to Agios Sostis (walks 6 and 7 — see the photograph above) are sandy beaches, with shallow waters that become very warm in the afternoons, if you prefer a warmer swim – at present there are many female sea turtles resting in the nearshore waters preparing to lay their first of second (every 15 days or so) of 120 eggs in the sand of the beaches. If you see a marine turtle in the sea, be respectful not to disturb them, the female turtles are conserving energy for reproduction, keep a distance of a few metres, and just enjoy watching these beautiful giants gracefully swim in the sea.
For stunning coastal scenery, you could drive, rather than walk, the Marathia coastal trail (walk 9) down to the rocky outcropof Point Marathia, where there is a sea arch and several caves worth exploring. You could also drive down to isolated Korakonisi Islet (walk 15), with deep cool waters and sea caves. Alternatively, if you have an offroad vehicle, you could detour off one of the car tours and drive along the first part of Cape Skinari Coastal Trail (walk 20) to point 7 which is a small isolated cove facing Kefalonia. Be certain to look out for sea turtles, monk seals and striped dolphins, along with numerous other forms of marine life. Whatever the weather this summer and autumn, you can still enjoy exploring Zakynthos!