Method of determining river water quality

A method of determining river water quality, comprising testing a body of water for the percentage of curved Melosira granulata X in all Melosira granulata therein. If X < 10%, the water quality is type I; if X is 10% ≤ X < 20%, the water quality is type II; if X is 20% ≤ X < 40%, the water quality is type III; if X is 40% ≤ X < 50%, the water quality is type IV; if X is 50% ≤ X < 60%, the water quality is type V; and if X ≥ 60%, the water quality is worse than type V. The method performs microscopic observation of the shape of Melosira granulata in river water, directly distinguishing and calculating the percentage component of curved Melosira granulata , thereby determining the quality and nutrition level of the tested river section.