In a large bowl, add the watermelon, blueberries, cucumber, feta and basil. Toss to combine.
In a small bowl, whisk together the vinegar, honey and olive oil. Season with salt and pepper to taste.
Pour the dressing over the salad and toss to coat.
Salad can be made up to 8 hours in advance. Store in the refrigerator in an airtight container until ready to serve.