While the cheesecake is cooling, prepare your berry topping.
Add the berries to a medium/large saucepan. Add the water and lemon juice. Cook over medium low heat covered to steam and pop the berries. (about 5-8 minutes) Stir occasionally to prevent burning.
Remove from the heat and use a potato masher to press the berries. Pour the berries through a fine mesh strainer set over top of a glass measuring cup to catch the berry juices. Use the back of a tablespoon to press the berries. Discard the pulp and seeds.
Rinse the saucepan if needed to remove any leftover seeds. Add the berry juice back into the saucepan and cook over low to medium heat. Bring the mixture to a simmering boil. Add the packet of Jell-O and whisk to incorporate. Simmer for 2-3 minutes. Remove from the heat and pour into a glass measuring cup.
Place the measuring cup into a bowl of ice cubes to cool for about 10-15 minutes. Stir occasionally. (You’ll end up with about 1 ⅓ fruit juices.)
You want the berry mixture to start to thicken and set up, but not be solid. It’s best if it’s thickened, but still liquid enough so it’s able to pour over the top of the cheesecake.
Pour the berry mixture evenly over the slightly cooled cheesecake. It will fully set when chilled in the refrigerator.
Refrigerate the cheesecake for a minimum of 4 hours or overnight.
Put toothpicks into the cheesecake top and wrap with a layer of plastic wrap. The toothpicks will help prevent the plastic wrap from sticking to the berry topping. Remove from the springform pan prior to slicing.
Use a butter knife to gently loosen the crust from the inside of the springform pan.
Top the cheesecake with fresh slices of strawberries, blackberries and blueberries before serving.