Preheat oven to 350 degrees.
Mix oatmeal, brown sugar and flour. Add butter and mix well. Spread mixture in 8 inch square pan, leaving 3/4 cup aside for topping.
Combine flour, salt, sugar, water, lemon juice and blueberries in saucepan and simmer for 5 minutes.
Pour over oat mixture and sprinkle with remaining mixture. Bake for 35 minutes.
Can be served with ice cream or whipped topping.