BLUE GUARD POND inhibiting algal growth. A preparation which easily and effectively protects garden ponds against excessive algal growth. It is harmless to fish, invertebrates and aquatic plants. BLUE GUARD POND creates a barrier against UV radiation, which inhibits unwelcome excessive growth of algae, including algae responsible for the so called green water and the deterioration of the general life conditions for fish and plants in garden pond. At the same time BLUE GUARD POND does not inhibit photosynthesis of other aquatic plants. It also gives water a sky blue colour which emphasizes beautiful coloration of koi and other ornamental fish in garden ponds.