If water COD is high what will effect to environment?

Question

this question is about biological treatment plant

Answer 1

the chemical oxygen demand (COD) test is commonly used to indirectly measure the amount of organic compounds in water. Most applications of COD determine the amount of organic pollutants found in surface water (e.g. lakes and rivers), making COD a useful measure of water quality

*** the higher the value then the higher the organic matter in the water and the less pure and clean the water is.