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.
Notes: Salad can be made up to 8 hours in advance. Store in the refrigerator in an airtight container until ready to serve.