Illegal waste discharge from livestock farms and suburban residences has been blamed for higher levels of phosphorus in Shanghai's water, the local environment authority has revealed.

According to an annual environment report issued by Shanghai Environmental Protection Bureau yesterday, over 70 percent of the city's waterways have failed to rise above the lowest rung of the National V standard in 2015. The density of ammonia nitrogen remained high, and the figure for phosphorus rose last year in Suzhou Creek and other major waterways.

"Phosphorus was recently included in Shanghai's plan to tackle water pollution in the next 15 years," said Zheng Kai, deputy director of the bureau's water division.

The chemicals do not directly harm human health, but have a negative ecological impact.

According to the report, Shanghai's general water quality in 2015 remained about the same as in 2014 — 14.7 percent met the National III standard for drinking, aquaculture and swimming; 13.1 percent fell into the National IV standard for industrial use and waterparks; 15.8 percent met the National V standard for agricultural and landscape use; and 56.4 percent failed to meet the National V standard.

"Due to Shanghai's location, its water quality can easily be affected by a pollution from upstream," Zheng told Shanghai Daily. "Water with a high density of ammonia nitrogen and phosphorus is also common in neighboring Jiangsu and Zhejiang Province."

The city's water authority said in earlier interviews that Shanghai will complete its sewage system and completely curb wastewater discharge in the next two years. By 2020, the majority of waterways should meet the National V standard, the bureau said.

The authority named 56 heavily polluted rivers around the city as major improvement targets at the end of last year. According to the working schedule, 60 percent of the rivers will meet the national water quality standard by the end of next year.