If canning, prepare a water bath canner, jars, lids and rings before you begin.

Wash and drain the blueberries. 

Add the fruit to an eight-quart (eight-liter) stainless steel or enameled Dutch oven along with two cups of water. 

Bring the mixture to a boil over medium-high heat, crushing the berries with a potato masher, then reduce the heat and simmer for 12 minutes, stirring often.

Line a fine wire-mesh strainer with three layers of damp cheesecloth. 

Place the strainer over a bowl, then pour the blueberry mixture into the strainer. Don't press down, as this can force some pulp into the syrup. 

Let the mixture stand for 30 minutes or until you've collected about 2.5 cups (625 ml) of juice (or until the mixture no longer drips). Reserve the pulp to make blueberry butter or for something else (you'll be left with around 5.5 cups or 1.3 liters of blueberry pulp in total).

Combine three cups of sugar and one cup of water in a large stainless steel saucepan, then bring to a boil, stirring until the sugar dissolves. 

Boil uncovered for 20 minutes or until the mixture reads 220 degrees Fahrenheit (104 Celsius) on a candy thermometer - stir often to prevent the mix from scorching. Then, stir in the blueberry juice and lemon juice.

Return the mixture to a boil, then reduce the heat and simmer, uncovered, for about five minutes. Stir once, then remove it from the heat. Skim off and discard the foam. 

Ladle the syrup into hot jars, leaving ¼ inch or .5 cm of headspace. Remove any air bubbles, then wipe the jar rims, center the lids on the jars, apply the bands, and adjust them until they're fingertip-tight.

Process the jars in a boiling water bath for 10 minutes - remember to only start timing when the water comes to a boil. After 10 minutes, turn off the heat and remove the canner lid.  (The canning time increases to 15 minutes if you're above 6,000 feet in elevation.)

Wait five minutes before removing the jars from the canner. Place them on a towel-lined countertop and leave them undisturbed for 12 to 24 hours. 

Check the seals, label, and store.