This document discusses a study on the impact of fine content variation in manufactured sand (M-sand) for G35-A concrete performance used in water retaining structures. The objectives are to identify current problems with using M-sand, examine property variations of M-sand in Colombo, study how fine content impacts G35-A concrete, and develop guidelines for optimum M-sand replacement. Testing showed compressive strength decreases with higher fine content. A 30% M-sand replacement produced the best results for G35-A concrete. Up to 15% fine content yielded satisfactory results for 70% replacement if cured for only 1 hour. Further study of clay content variation and particle shape is recommended.