Pick the right time and you can have this swim to yourself. Jump in via the slipway on the south shore then swim parallel to the shore east or west along Hadleigh Ray.
It will be a less energetic swim around 30 mins before high tide. Best to wear a bright-coloured cap and take a tow-float to be seen by the numerous boaters. There is a large car park but no toilets or cafe on the island itself. Leigh-on-Sea has the closest facilities (some may be available at the Golf Club at the entrance to the island).