In a small saucepan, combine blueberries with sugar and water. Bring to a simmer and cook 5 minutes. Mash slightly with the back of a spoon or a potato masher. Cool completely.

In a large bowl, fold together whipped topping and lemon yogurt. Swirl in 3 to 4 tablespoons of blueberry mixture and transfer mixture to crust.

Refrigerate 6 hours, or overnight.