A method for decreasing, or restricting the multiplication of, algae in eutrophicated lakes and ponds regardless of the depths and sizes of lakes and ponds, and a device therefor. Floatable light-shielding members (1a, to 1e) are allowed to float on the water surface (WL) of a lake (L) where algae grown abundantly due to eutrophication should be decreased or restricted in multiplication to shield the water surface of the lake (L) from light to thereby provide a specified shielding rate, whereby photosynthesis of algae is obstructed and algae can be decreased or restricted in multiplication.
展开▼
