The researchers used a method called the weighted arithmetic water quality index to check the water quality of Anwai river in Delta State, Nigeria. They looked at different factors like pH, dissolved oxygen, turbidity, and coliforms to see if the water is safe for people and aquatic life. They found that the water in the river is not good quality and could be harmful to health if used without treatment. The main issues were high levels of contaminants like phosphates, nitrates, and coliforms, likely from human activities and sewage. Overall, the water quality index showed that the river water is poor to very poor at all three stations tested.