Combine berries, lemon juice, water, and sugar in a small saucepan and stir.
Bring mixture to a boil.
Reduce heat to medium-low; gently boil 10 minutes or until sauce thickens.
Stir in butter.
Spoon 1/2 cup yogurt into each of 4 bowls; top each serving with about 1/4 cup sauce. Serve immediately.